This involves making a small pocket inside your partners mouth (Probably with cling film etc) then fill it with a small amount of poo. Then as you are about to bolt after fucking your partners mouth, thrust really hard and break through the poo-pocket thus filling her mouth with spunk and poo milkshake: Hence a "Hot Lunch" Simple really.
Mac: "Hey Soph, You wanna have a Hot Lunch today?" (He he he)
Soph: Oh yes please, only no sweetcorn this time, it gets stuck in my teeth.