Usually occurs when the character is talking over a com-link or radio using an earpiece and are receiving instructions or intel for a mission. The character usually has a weapon in one hand and their other hand to their ear. Usually following the character touching his earpiece, BIG EXPLOSIONS happen or a lot of enemies engage the player in battle.
This is also a basis for the "Tough Guy" stereotype.
This concept largely originates from the codec conversations in the Metal Gear series. G.I. Joe: The Rise Of Cobra, an otherwise unremarkable game, spiced up the earversation recipe a little, when certain characters are shown using their left hand to cross their chest and use the earpiece in their right ear.