When a girl is wearing large, men t-shirts that do not fit her, while going out in public or to a party.
Its Friday night and your at a party looking for that fine girl. Your friend comes up to you and points out the weird nasty girl. You ask who and he says the one (macked out).
We totally macked out that 'whatever', showing it taken over-the-top...like a kitchenloaded with top-of-the-line appliances, PLUS some other cool stuff.
When one gets punched in the face so hard that you could compare the force of it to a Mack truck coming full speed. Basically another word for getting knocked out cold.
Jon: Yo, did you see that street fight earlier today?
Marco: Yeah bro, Tony got macked in the face! He couldn't even get up.