Slang, insult; In reference to a woman of an extremelyelastic vagina, usually from being overly sexually active, insinuating you could insert two hands and clap.
"Joyce's neighbor was such a 2-hander, she used to bring home 3 guys to bang every night!!"
It is as it sounds: a Man (yes, capitalized for this instance as only a true Man can pull off this maneuver) unzips his pants and takes his dick in both hands and slams it down on the table to prove his point. This is only to be used in circumstances where without slamming the cock on the table, the story, argument, etc. would be laughed off otherwise.
The old man stood in front of city hall telling the police chief about his 2 Handed Hammond. I showed this hooker my 2 Handed Hammond; She said it was the biggest she'd ever seen.