Again, not an orthodox joke with a punchline, but this was an actual occurrence of when my girlfriend cheated on me and my indignant reaction:

I was just reminded of an incident while telling a story (this happened in 2006):
I'm waking up getting ready to go work out and hit the rock climbing gym looking for my gear. My gf at the time comes stumbling in still drunk from last night and she tells me, "I went out with my friend, got drunk, and fucked her brother."

I raised my eye brows in shock, and i approached her furiously and said, "Why the fuck did you...." interrupting, she says "im sorry i cheated!!" and i say "i wasn't finished. I'm asking why the fuck did you put my rock climbing shoes outside???? The sun will make the leather shrink, damnit!" I drive the point further, "now i gotta stretch these things out again, i'll be back in 10 hours, think about what you've done."