I stumbled upon this awesome post over at Mormon Mommy Wars. It has a bunch of "funny things that happened at church" with an emphasis on crazy fast and testimony moments. Give it a looksee.
Our ward in Provo was always pretty calm. I don't remember any real crazies at church. One time one of the priests was giving the closing prayer in sacrament meeting and started giving the sacrament prayer instead. As a missionary in South Korea I somehow avoided having too many weird experiences at church. We never had anyone crazy wander in, although we did have an unofficial janitor who lived in the basement of the church. One night we were having an open house at the church and he wandered in drunk. He was an older guy who had learned English from the soldiers during the war, so he knew some choice words which he proceeded to use. I can't remember how my companion and I convinced him to settle down, but we eventually got him to leave. It wasn't long after that that they found him some housing elsewhere.