boner effect
When the button portion of one's jeans is caught underneath the belt, pushing the lower zip section of the trousers outwards, creating the illusion of a boner.
Frank: Ay look Bills got a hard-on
Bill: Nah bruv (correcting his jeans), it's just the boner effect. Don't get gassed.
Bill: Nah bruv (correcting his jeans), it's just the boner effect. Don't get gassed.