I studied for multiple semesters with the Benedictine monks while in college. Particularly, I spent three months studying under an old testament theologian who did the translation for the new St. John's Bible. He taught me about biblical sources, about how a particular translation could change an entire passage's meaning, etc. I loved learning this stuff and began to independently study Islam, Taoism, Buddhism, and LDS. Religion became purely academic for me.
I grew up very catholic, and was becoming increasingly frustrated with the "lack of reward" I was getting by being a good catholic. I was getting somewhat stressed out because I was literally blue balling myself following the goofy rules and pissed that God didn't reward me with some blonde haired knockout virgin. Finally one day I just said screw it, began dating a girl I was into but wasn't "that" into, had sex, and realized life is way more ####### fun with some dyonesian infusion.
All this same time I was studying philosophy and political theory, and found myself looking more logically at issues (not through the religious lens) and realizing that a lot of religious dogmas were pretty ####### stupid and borderline bigoted. I began to look at what I considered "normal" behavior - like evangelism, going to church all the time, etc. - and realize it was pretty goofy.
For the above combination of reasons, all happening through the span of college, caused me to go into college a devout, god-fearing catholic and walk out an atheist.