To be ridiculous or over-the-top, usually in a comedic way.
"Class was really boring today until Tom stood up on his desk and did a jig. He really knows how to ham it up."
"The actor was supposed to fall over and die, but he hammed it up too much and got fired instead."
In video games, to keep a person or object in midair by hitting it multiple times. Especially used in fighting games like Super Smash Brothers.
"Alex can juggle Sandbag like nobody's business. He kept it up for more than 5 minutes!"
