version of shut up, shut it, shut your trap. do not confuse with damn it or dammit. think how a dam blocks the water from flowing down the river. hopefully if you tell someone to dam it, they will put a stop to their diarrhoea of the mouth.
parent: clean your room. now!
unruly teenager: no! dam it mum!
parent: dont speak to me in that tone of voice! dam it!