Referring to the popular McDonalds sandwich ("My saucy celebration" as advertised on posters) which can be mistaken for the climax of sexual intercourse.
Last night me and my girlfriend had a saucy celebration in bed!
A McDonalds sandwich and a surprisingly fitting euphemism for sex.
"Hey you wanna go get a saucy celebration? I've heard McDonalds has them again."
"Hey babe, let's have a saucy celebration tonight"
"My saucy celebration had too much sauce and it spewed all over my face"