So you're eating in a Mexican restaurant and the mariachi band strolls over. "Any requests, senor?" and you really, really want them to sing "Cucurrucucu Paloma" (or maybe "Jesusita en Chihuahua").
How much money do you tip them per song?
This doesn't have to be limited to mariachi -- how much do you tip the guy who sings you "That's Amore" at the cutesy Italian place with the accordion, or the violinist at the fancy restaurant, or...
I can't believe I'm asking this question, because I used to be a singing busboy at the Macaroni Grill, but that was well-nigh fifteen years ago and the amounts have undoubtedly changed.