Someone who is ridiculously dumb, make
an ass of themselves, and hasn't got a clue
about what's going on around them. However, tools are usually used
and kept around for either entertainment purposes (ie. getting them to do something really stupid for laughs) or for other things
Phil: Hey, that
Dick guy, he's a fuckin' tool! He sings "I'm a Little Tea Pot" when I tell him to.
Bob: Yeah, that
's the only reason we keep that