Black people singing country songs. Something about this just fills me with delight... maybe because it suggests that the melting pot is really working.
Exuberantly bad singers. Mrs Miller types.
When two or three nervous singers band together to do a song as a group.
When you can't tell how much of the singing you're hearing is from the people onstage, the people in the crowd or the prerecorded voices.
When gals do songs that are written for guys and vice versa.
My friend J'mel's story about singing "Thank You" by Alanis and making Pokemon characters the subjects of his thanks. "Thank you Pikachu, Thank you Geodude..."