Calling dibs is the quick, cheeky way to stake your claim before anyone else nicks it. You shout it over a seat, the last chip, a lift home, whatever, and the group usually treats it like a sacred playground rule. It’s not legally a thing, but socially it’s powerful. Ignore someone’s dibs and you’re courting a proper strop.
"Dibs on the last pizza slice. Nah mate, you can’t call dibs from the sofa. Watch me, I just did. Touch it and you’re buying the next one."