From Meet the Medic, which is completely awesome, and made by the awesome people at Valve.
That scene made me happy for multiple reasons. Mostly the hilarious expressions, and also it's fun to see the Engineer and Sniper together in one scene. They're awesome.
As soon as i saw those expressions in Meet The Medic, I knew I had to screencap for the whole world to see XD
XD Loved their expressions!