The startled feeling you have when you realize, too late, something you should/could have done differently, and usually blurt out,"Aw, shit, I could have {insert missed action here}";often occurs while gaming.
We were playing Munchkin last night and I had a shitpiphany when I remembered, too late, that as a Ranger I could have made the cyclops into a steed instead of fighting it.
Hey man, you remember that scene in Point Break when the chief tells Utah that he's young dumb and full of cum? I just realised thats so much more offensive if you say it about a lady.
shit·e·piph·a·ny shit-ih-pif-uh-nee
A sudden, intuitive perception of or insight into the reality or essential meaning of something, usually initiated while sitting on the toilet taking a big shit. PER RSMM