The phrase that is used when people do something terrible for the sake of a prank. It's mostly used by trash youtube pranksters.
GUY 1: What the heck dude? You broke into my house, dressed up as a killer clown, killed my girlfriend and chid, stole my money, leaked my nudes, and set my dog BoBo on fire!
What you say when you've verbally or physically assaulted someone and they get mad and attack you. If you've ever had to say these 4 magical words, that means you suck monkey cock at doing pranks and probably don't even know what a prank is.
Mark continued to yell out "bro it's a prank!" as the frustratedblack man attacked Mark for yelling out racial slurs at him.
White Kid: "Ayo, nigga"
Black Guy: "What you say to me, nigguh? (Starts pushing the white kid)
White Kid: "Its a prank! Its a prank!
Black Guy: "Ahh, you're just fucking with me, I got you.
White Kid: "Yeah, I was only fucking with you, pff"