The bottom line is - sing what ever you like (or can remember ?!?)- my own song selection criteria is based upon the mood of the club that I am attending. If every song has been a "Slit your wrists" type then I will try changing the mood by singing something funny, likewise if all the songs are humorous - then I'll sing a "hanging" song (eg."McPhearson's Farewell")ALWAYS SING SONGS THAT YOU LIKE !!!
The most outrageous song that I sing is [to a very mixed response ?!?] "Benny the Bouncer" by Emerson, Lake & Palmer, from the album "Brain Salad Surgery" - If I can get away with that one - then anything is possible !!
PS. - Try singing "Hangman/Prickly Holly Bush" in calypso style, it's easier than you'd think, it's a joy to sing and the folkies love it (and it is Traditional) !!