When a man goes into a toilet to take a shit. He puts a carrier bag on the floor and his friend steps inside it. Then the man taking a shit starts sucking his cock. So, if some looks underneath the door it looks like someone is sat taking a shit with their shopping between their legs.
Guy 1 - fancy going cottaging?
Guy 2 - Let me get my carrier bag
Guy 3 - What are they doing in there? let me take a peak under the door. Ahhh He's taking a shit, must of just got back from the shops.