As well as my "folky" side, I play in a band. One of the songs my brother sings, is Vince Gill's "Whenever You Come Around." Every time he sings the line "I'm standing here holding the biggest heartache in town, whenever you come around." I can't help but change it mentally to something entirely rude.

"I'm standing here holding the biggest hard** in town,
whenever you come around."

Likewise a few years back, we were doing an old Statler Brothers song where the lyrics went:

"But for too long you've kept it in,
And it burns a hole down deep inside."

At which point I made a very loud farting noise. He virtually collapsed across his drum kit with laughter. End of song, and he never sang it again.