To be beat (adj) In normal terms ‘beat’ would be used meaning ‘to win’Manchester United beat Liverpool, or ‘to hit’ Marko, stop beating your brother, however, in slang or everyday English it means something completely different. If you hear your friend saying I’m beat, it means he or she is very tired or exhausted.
Example 1)
“Do you want to go out tonight? There’s a cool new rock bar that’s just opened.”
“Sorry, I can’t. I’m beat and I have to wake up early tomorrow.”
Example 2)
“You look beat, what have you been doing?”
“I’ve been helping my dad in the yard all morning.”