Hayley Atwell! Doing 10-second lip-sync videos with other actors!
Here's my favorite, because I am extremely into their faces here.
Then there was a "war" with Clark Gregg and Chloe Bennet (from Agents of SHIELD), which is compiled, slightly out of order, at YouTube (and is missing this one). (If you want chronological order, see the link I'll give at the end.)
(Previously there was her and the guy who plays Ward, whose face is very appropriate for Vanilla Ice.)
And then, today, there were these glories: mic drop, celebration. Amazing.
(Marie Claire has the "war" in chronological order but spoils today's events.)