One time, I was at a concert for New Years. Most of my friends at the time were Christians, so it was a concert behind a church of all Christian bands.
There was a band that were not at all Christian but they got along with all of the Christian bands so they were often at a lot of Christian gigs in the area. They were like a punkier SOAD.
Anyway, as they were warming up, the guitarist starts playing a random selection of riffs from Reign in Blood. I was possibly the only person in the audience who recognised them. Cheeky bastard.