I don't think Tijuana is much of a place to go for things like wet t-shirt contests, if you're talking civilian American or Mexican-American chicas? Revolution has a few bars that cater to the American tourist and 18 to 21 year old crowds hang out on weekends. You can't miss the bars on Revolution, you'll hear them before you see them.
But now I understand the kids 18+ college kids more often go to Rosarito Beach, also very close to the border slightly more than 10 miles. They have 3 or 4 major bars like Papas & Beer, where I know during Spring break they were advertising wet-T-shirts contests. I don't know what they are doing during the weekends now, but I'm sure you can always find a little "girls gone wild" behavior on most weekends, but you should be young, and have a little 'game' with you if you hang out at these places.