I have a real problem with that-- a few years ago Emily & I were invited to a Christmas party at our Priest's house ( I was for some years a choir singer... ) and he, she, and I ended up leading the group in singing popular Christmas songs.
Only problem was, I had, ahem! reworded them into X-rated versions, and I had an awful time recalling the straight lyrics in time to sing the dam' things...
BWAHAHAHA!! I've got a similar problem when I get together with my bandmembers to practice...when I sing my reworked lyrics, it throws them off becuz they start laughing, so I have to sing the originals to keep time and I have to have the original lyrics right in front me 'cuz my lyrics have pushed the originals outta my noggin.
The Trials and Travails of a Parodyist, I reckon...
LOL and FReegards...MUD