Can't do it!

An exclamation made when you simply can't do anything anymore. Basically giving up.

a phrase when someone can not do something

a statement used before the classic;
THIS DICK!, or DIS DICK!

Fantastic Canadian-made older kids' show aired during Nickelodeon's infancy. Involving snot jokes, barf jokes, fart jokes, and other similar hoohah, it was notable for naming one of its castmembers "Moose" despite the fact that she was a young human female.

A show that started out on local TV in Canada on CJOH.
Executives of a station called "The Pinwheel Channel" in the US happened upon it and decided it was just what their station need. Then The Pinwheel Channel became Nickelodeon.
Then they had a hit.
Not only boosted the lulling stations ratings but also gave them their trademark slime scheme. Nick doesn't acknowledge this, perhaps because publicizing it will do no good to them. The slime would fall on someone when they said "I don't know." Water would also fall on someone who said "water."
It ran in the US from 1981-1990. It was such a big hit in the US, it left Canadians scratching their heads. Most Canadian children found the show disgusting and it never had a wide audience in its homeland.
Supposedly was cancelled because the show went through kids like a revolving door on crack and it was a tedious task to send royalty checks to 200+ different children.
Alanis Morissette appeared on about six episodes of the show in 1986, as a minor character.

Meaning the person is tired of living and wants to commit suicide

what I say all the fucking time.