Definitions by Steel Toe Joe

gtm 

Gun To Mouth. Expresses dismay, exasperation, world-weariness.
Stronger than smh (shaking my head).
Unlike kill me now or shoot me now, gtm implies that the speaker plans to pull the trigger himself.

I just heard Marvel signed a contract for 3 more Ant-Man sequels. gtm

gtm by Steel Toe Joe May 13, 2016