So, most restaurants are not gonna be impressed if you decide to start grilling your own food on their premises. They're a place of business. Dietary ethics aside, what you did was fucking rude. Not a prank, literally just rude. Most restaurants have signage saying not to eat or drink food from outside, because they're not free seating; they're a place people go to buy food.

Secondly, if this is your idea of a prank, you are simply just not very funny. Most "prank" YouTubers are like this; it's not funny, at best it's just mindless disruption and at worst it's actively cruel. There was one guy who "pranked" his girlfriend by making her think that her beloved cat had fallen from their high-rise apartment's window and died. She was inconsolable. Is that the sort of genre, of community, you want to be a part of? I get that you're young, and seventeen year olds are not exactly known for their critical thought or reasoning ability, but come on now. Maybe don't start a hobby that requires you to make other peoples' days worse by it's very nature. It's not a joke unless everyone's laughing.