#1 When you nonce multiple girls that are normally below England's age of consent
#2 When you commit credit card fraud and/or theft despite living in a super rich area
#3 When you may or may not have fucked your own cousin whilst being fully aware that they are your cousin and vice versa.
#1 Oh Crap I'm McGilling this girl 4 years younger than me. I hope the police don't find out.
#2 I think it was a good idea to McGill this random Iphone i found on the floor and sell it for as much as i can
#3 Man, I just McGilled her... It was great!!
when you're holding up your phone and making faces at it, as though you are taking a selfie, but you're really taking a picture of the person across from you or the wall or anything else that seems interesting but you don't want to be caught dead taking a picture of.
This action is often made more convincing by wiggling the eyebrows or opening the mouth, to pretend you're trying to get a Snapchat filter to work.
FRIEND A: "Did you just take a stealthie of me?"
FRIEND B (turning phone around): "no I was just using snapchat's new filter, see?"