Literal translation of shirt: "(I (implied)) Eat ass."
(Side note: Don't ever use/say this. #smh)
Lifted from: https://twitter.com/reijisano551
@troubleMoney But yes, "taberu" 食べる is the verb used "to eat" something. eg I eat current every Friday. 毎週金曜日にカレーライスを食べる。