shud it

Telling someone to be quiet in a light bantering tone.

Can be used to counter someone when they've been teasing you.

Can be used in silly mucking around behaviour.

Example One
Marcy: "So Judy, are you going to wear mismatched shoes again today "
Judy "Shud it" Marcy

Example Two
Person One: Sooooooo when are you going to see Markkkkky againnnn heyy...
Person Two: Shud it woman

Example Three (silly behaviour)

Person 1.... nah nah nah you suck
Person 2.... shud it