to sleep with one eye open

(informal, litotes) not to feel too at ease, i.e. to be scared out of one's wits

(dated) to threaten, to guarantee that there will be hell to pay, that there will be severe retribution, that there will be trouble

(transitive) not to let out of one's sight, not to take one's eyes off, to keep an eye on

(vulgar) to do fuck all, not to do a damn thing, to do nothing

(informal) God forbid!

(informal) and that's not the half of it!

to be something to which one wouldn't say no, to be something that one wouldn't mind, to be most welcome

to be no sucker, to not be easily taken in, to not let oneself be fooled easily

a leopard cannot change its spots