Happened to a friend of mine
Except he didn't know his girlfriend had just been with someone else until they started getting down to it. It put him right off.

"I didn't fancy stirring someone else's porridge." was how he put it.
(Che Grimsdale Best before:, Fri 19 Feb 2010, 14:53, 1 reply)

I got a blowjob
off some classy young lady in a club (well, the car park) years back and then went back inside, in the 2 mins of me getting to the bar and back to her she was snogging another bloke, Stirring my porridge with his tongue. Poor bloke.
(Kip, Fri 19 Feb 2010, 15:36, closed)

I wouldn't be able to resist going over
and saying, "I've just had my cock in there."
( sandettie light vessel automatic New Twitter - @bollocksreally, Fri 19 Feb 2010, 15:53, closed)

I very nearly did
but thought in the reverse situation, I'd rather not know, so left them to it.
(Kip, Fri 19 Feb 2010, 15:57, closed)