A phrase used on Internet forums to counter the vast range of unverifiable claims made by users. Often these claims involve personal brag-worthy accomplishments, extraordinary or rare sights/occurrences, and tales relating to alcohol or drug use.
Guy 1: Dude, I drank four bottles of bourbon last night, then hooked up with 4 chicks at the same time, then Donald Trump came to my house and gave me a million dollars!
Guy 2: Pics or it didn't happen.
A phrase used primarily on online forums stating that the person refuses to believe the thread creator's claim unless it is shown by a photograph for proof.
I got 73 kills in a single game on Call of Duty 4 and it wasn't even on Shipment.
Reply: Pics or it didn't happen.
Pics or it didn't happen is used when someone makes a very far fetched statement about something. See example.
Teenager1: So brah ask me what I did over the weekend
Teenager2: ok....what did you do over the weekend?
Teenager1: I went over to this girls house and I fucked her and then her mom walked in on us and we had a threesome
Teenager2: Pics or it didn't happen looser!
Figure of speech, sarcasm. Used when someone has described something so vividly that you really don't need to see pictures to fully understand.
That guy just spewed his supper all over the sidewalk. Looks like he ate hot dogs and Fritos, and maybe had some sort of grape soda to drink...
Ewww, gross! Pics or it didn't happen!