The cut down is a hand gesture use to symbolize a "diss" or a "put-down". To administer the cut down, you extend your left arm fully to make a 20 degree angle or so, to your chest. Then slide your right hand from your shoulder to the end of your left hand. You can also say the word cut down while doing the motion for added effect.
Garrett just used the nastiest your-mama joke known to man on Ryan, so I furthered Ryan's shame by doing the cut down.
The act of bringing a person down with a short, nasty twist on words when they are excited or proud of themselves.
Also, patronizing someone into submission is another technique in cutting-down.
Guy 1- Oh my God, this is the best thing ever! Liste--
Guy 2- Oh! Is it?! IS IT YEAH?! *turns away*
Male Doctor- No, I'm serious, my incision- you wouldn't believe how small it was!
Female Doctor- Yeah that's what she said. *walks away* Cut down!
Male Doctor- Hey!... Shut up.
. This is a variant of shutdown, used more commonly in Canberra Australia. Shotdown is also used.