You'd be surprised. When Houston and Texas were in the old SWC, during the Jack Pardee coaching era at UH, Pardee was using the Run & Shoot offense, the brain child of Mouse Davis and June Jones. No tight ends and only a single running back on offense are the way you run it. Houston went up to Austin one year and beat Texas 66-15. Texas never forgot about it.
Several years later after the Cougars and Longhorns had parted ways when the SWC broke up in 1994, they had a home and home series in the early 2000's. The year Texas came to Houston they were pissed because Houston had quit playing their home games in the Astrodome and had returned to their old stadium on campus called Robertson Stadium. It had been refurbished but still only seated about 28,000. Texas demanded that additional seating be erected in the end zone to accommodate more of their fans. Houston did it, but it probably only added another 2-3,000. Texas rolled up a big score of something like 49-12. After the game the Texas coach was quoted as saying they deliberately ran up the score because of the game in Austin back in 1988, and because they had to play in this crappy little stadium instead of the Astrodome.
For whatever reason, teams carry these grudges around with them for a long time, especially when they involve former conference rivals. As far as our AAC opponents are concerned this coming season, we are going to be playing them as former conference rivals, because we announced we're leaving the conference. Be prepared for some epic beatdowns in football and basketball. Geno's team will have to make up for them.