Most rivalries I can understand. Take Kentucky-Louisville, for example. It’s largely a rural vs. city thing, and each side has stereotypes of the other that they will trot out at the slightest provocation. Sometimes it’s fun, sometimes it’s ugly. But at least it’s fairly easy to comprehend.

But the St. Xavier-Trinity rivalry baffles me because so far as I can tell, the two schools are very much alike. When one looks in the mirror, it sees the other. In horse racing, they are 1 and 1A. They are the identical twins that outsiders find impossible to tell apart.

Generally speaking, the students at each come from the same pool of white Catholics families which are middle-to-upper class economically and socially. They don’t even have much geographical separation, Trinity being located in the heart of St. Matthews and St. Xavier on Poplar Level Road near Eastern Parkway.

In many cases, St. Xavier families and Trinity families live next door to each other or mingle at the same parishes. If there are certain character traits that stamp somebody as a “St. X man” or a “Trinity man,” they are invisible to the naked eye.

Yet when the two get together for a football game, as they will again Friday night at Cardinal Stadium, the rivalry erupts like a dormant volcano and spills its hot green lava across the community. To listen to both sides talk, you’d think St. X was Venus and Trinity Mars, to borrow a phrase.

I don’t get it.

I don’t understand why normally sane businessmen, many of whom are my friends, begin rooting around for their high school letter jackets to see if they still fit. Right before your eyes, they change into teenagers again. They seek out old high school buddies so they can attend The Game, as it has come to be called, in small packs fueled by testosterone and adult beverages.

Consider Tony Vanetti, co-host of the popular “Afternoon Underdogs” show on 790 radio. He’s a Trinity man and proud of it. Although hyper is a normal state for Tony, who can get himself worked up over just about anything, he throws it into another gear before the St. X-Trinity game.

Across the hall at WHAS 840, Terry Meiners, a St. X man, takes a more detached, bemused view of the buildup to the game. Yet Meiners comes from a St. X family and, down deep, he doesn’t want the current Tigers to give The Beasman – a stereotypical Big Blue fanatic, by the way — anything to crow about.

I’m old enough to remember when there was no Trinity – it didn’t graduate its first class until 1957 – and when St. X-Flaget was the big local Catholic rivalry. That one was easier for me to understand because there were very real socio-economic-geographic differences between the two.

Flaget was located in the West End and generally drew its students from the working-class families who surrounded it. Back in those days, Louisville was more of an industrial city than it is now. We had vibrant breweries (Falls City, Fehr’s, Oertel’s 92) to go with the distilleries. We had Reynolds Metals and other factories that closed years ago.

But thanks mainly to coach Paulie Miller and a remarkable group of athletes, Flaget arguably had the state’s best football program in the 1950s and ‘60s. Its rivalries with Male and Manual were every bit as important as the one with St. Xavier. Flaget was the school that produced Paul Hornung, Sherrill Sipes, Howard Schnellenberger, Rick Norton, Oscar Brohm, and may others who went on to become college stars at Notre Dame, UK, U of L, and other major schools.

However, white flight from the West End led to the demise of Flaget, which closed its doors in the early 1970s. It wasn’t really replaced by Trinity, because its students were spread among all the county’s other Catholic high schools, but Trinity was the one that emerged as St. Xavier’s No. 1 challenger for athletics supremacy.

I’m not sure when the rivalry morphed into The Game. Maybe it was the first time attendance hit the 25,000 mark. Mostly, though, it just happened naturally without any contrived hype or planning. To keep it that way, as pure as possible, the administrations at the two schools have resisted most overtures from commercial sponsors, including ESPN and the big shoe companies.

Still, I don’t get it.

How can people who have so much in common work up such a magnificent hatred for the other side? When a St. X man insults a Trinity man – or vice-versa – it’s like he’s insulting himself because the two schools are so close in their missions, values, and philosophies.

I can only offer a couple of theories.

First, there’s the generational thing. Fathers who went to St. X or Trinity can be almost pathlogical about wanting their sons to attend the same school. I have known Trinity men who get depressed – really – if a son insists on going to St. X. And vice-versa. It’s a guy thing. Passing the torch from one generation to the next is very big for both St. X and Trinity grads.

Second, it’s simply a part of man’s nature – his dark side, if you will – to be competitive. More so than women, although the gap seems to be closing, men have a pathological need to compete and be No. 1.

In Catholic football, this manifests itself early in a child’s development. If you have never been to a parochial-league championship game, you should go sometime to watch the parents, not the kids. Pay special attention to the overwrought fathers who scream from the bleachers or patrol the sidelines.

These are the same guys who want to collar you and talk about a talented seventh- or eighth-grader at some parish or the other. This was going on among Catholics long before it spread to the general population. Now, sadly, recruiting has become an industry unto itself and the “gurus” are ranking fifth- and sixth-graders.

Anyhow, most men have to compete about something. It is not the nature of the beast to just get along. The urge to be No. 1, to feel superior, to dominate is older than the concept of Tarzan beating his chest after knocking out an ape. Bookmakers love The Game because grads bet with their hearts, not their heads.

Or maybe it’s just that Trinity and St. X are literally in a class by themselves. They have to work up a good hate for each other because public-school football just isn’t what it used to be back in the days when Male-Manual was “The Game” or “The Rivalry.”

But these are just my theories, crafted from listening to St. X and Trinity men over the last five decades. What do you, dear reader, think? What distinguishes a St. X man from a Trinity man? How do you tell them apart when they’re not wearing their letter jackets?

If you can help me understand, sent me e-mail here at Catholicsports.com. Please refrain from vulgarity and profanity. And be sure to check your spelling and grammar. I’d hate to be able to say that I can tell one side from the other because one obviously has better English teachers.

One more thing: I like St. X Friday. Make it 28-27.