Sick as a What?

The expression "sick as a parrot" is apparently something to do with football, and more than that I can't tell you. (When it comes to football, I get that there's a ball and some feet involved, but after that it all becomes a bit hazy, apart from the homoerotic aspect, which is crystal clear.) This is a book cover from the days when I used paint and stuff.

I've never actually seen copies of most of the books I've done covers for, incidentally. Point of interest.