You twist your thumb, unnaturally behind your pointer finger knuckle, to the point where your thumb can go no further. Then you make a fist with the rest of your fingers, and it looks absolutely awkward.
Person 1: Hi, my knee is really killing me today.
Person 2: Man my head is killing me, we drank too much last night.
Person 3: Wow, my ass is really sore from all that butt sex.