When a soldier hits another soldier's kevlar helment with his own kevlar. Since the cover is usually green camo it looks like to turtles rubbing together, hence the name. I t isn't used much anymore because most soldiers are running around in desert uniforms now because of OEF and OIF
When the girl you are fuckin just wants to lay on her back while you stick your cock in her shell. She Will refuse to do any sort of work and rather just last there legs wide open and motionless. (Sometimes groaning like a turtle during mating *see youtube*)
"baby im tired you get on top and work it...noooo i jus wanna lay hereeeee" YOU HAVE A CLASSIC TURTLE FUCK ON YOUR HANDS