"Nine martini nightcap" joke

(As told to me by a bartender, original source unknown.)
A tired looking gentleman walks up to a bar and asks the bartender quite
explicitly for nine double martinis, extra dry, hold the olives, and to
serve them all at once, right away. The bartender gives the man a curious
look, but to no effect, and proceeds to mix and pour the man's request.
The gentleman picks up the first and turns it up quickly before the
bartender can finish pouring even the second one, and proceeds to drink
each one in turn. Finally, the bartender has to ask.
"Why all the drinks?"
"Celebrating!"
"Oh? What's the occasion?"
"My first blowjob."
"Well, congratulations. Let me give you one on the house to make it
an even ten."
"No thanks. If this doesn't get the taste out of my mouth, another
one won't help any."