What does to gib someone mean?

To gib someone in the most "normal" sense i.e. "You really gibbed him."

It is to blow apart and dismember a individual with a weapon of some sort, although this is the definition of it in video game terms. From my experience this is where it is most commonly heard, but this is a slang meaning of gib. I would advise you look at a dictionary since there are several different meanings of gibbed. both slang and other wise, for example it means a castrated cat and several other things.

Please excuse any bad grammar I wrote this relatively late at night for me, and it was a long day.

A side note. Gib and gibbed are essentially the same thing just used in different tenses.