The posting of private email threads in order to bring a shower of shit down upon the people involved in the messages.
"Ima post this Threadgate and everyone will see what a douche you and your friends are", or

"Ima send this Threadgate to your worst enemy so that they can post them all over the internet and make ya'll look like fuckin gossiping idiots with too much time on your hands"
by Dirty Sally April 09, 2010
Get a Threadgate mug for your mate Julia.