Green’s Dictionary of Slang

1. (US campus) tired out, exhausted.

1972		Eble Campus Sl. Oct. 2: eat up – temporarily physically unattractive [...] Carol looked eat up and felt worse.
1996		Eble Sl. and Sociability 44: The meanings associated with many of these pictures of destruction are scattered in subject area — [...] eat up ‘fatigued’.
1997–2001		Online Sl. Dict. 🌐 ate up adj 4. burnt out or exhausted from the use of illegal drugs, usually ecstasy. (‘He’s really ate up from the rave last night.’).

2. disorganized, messy, all over the place.

1997–2001

Online Sl. Dict. 🌐 ate up adj 1. not ‘squared away’ (i.e. not organized or prepared, a mess.) If someone does something poorly, they’re ‘ate up’. Origin: the United States military. In the example phrase, ‘soup sandwich’ is an example of something messy. (‘You’re all ate up like a soup sandwich!’).

3. (also eat/ate up with the dumb-ass) strange, unusual, crazy.

1988		T. Harris Silence of the Lambs (1991) 36: You come talking that mushmouth, people say you eat up with the dumb-ass, girl.
1997–2001		Online Sl. Dict. 🌐 ate up adj 2. strange, stupid; WEIRD. (‘Don’t worry about Eric, he’s just ate up.’). [...] ate up with the dumb ass adj 1. strange, stupid; WEIRD. Origin: American rednecks. (‘Don’t pay any attention to him, he’s ate up with the dumb ass.’).

4. keen on, obsessed with.

1997–2001

Online Sl. Dict. 🌐 ate up adj 3. interested, to the point of near obsession. (‘He’s ate up about the military.’).