Grew up a Utah fan, watching games with my dad who is a Utah alum. Even one of those who stormed the field in '93 and was referred to by Gomes as a future gas-pumper.
But when it was time for college, I looked at a bunch of schools (almost exclusively out-of-state). BYU was my safety school (Utah wasn't really under consideration), but ultimately the one I went to due to financial reasons (a half-tuition scholarship to Duke sounds great until you realize that still leaves you on the hook for $30k/yr plus housing and food and books and the like; BYU was cheaper and gave me the full ride that covered literally everything).
So I enjoyed my time at BYU, but even at the start wasn't a BYU fan so much as a Utah fan. Went to games though because my friends were going and because I like football. And while I'm there, of course I'm going to root for the team with my friends, so became a BYU fan.
Caveat on that is that I never started to hate the Utes either - still enjoy them being successful even now. Also, I was there in the rough Crowton years (2002, 2003) before my mission so I never developed quite such blue goggles as people who had better experiences. After my mission I found a better school fit for me, but I still root for BYU.