hold my beer
1. (originally) The act of handing one's drink to another before attempting a dangerous stunt--that has never been before attempted; this often involves an element of stupidity.

Person: OMG, that guy just performed a perfect back three-and-a-half somersault pike dive!
Drunk: Pfft! That's nothing--hold my beer!

Drunk 1: No one's ever tried riding from the roof on a sheet of metal.
Drunk 2: Here. Hold my beer.

2. (online)
a. Video clips of people performing dangerous feats that they often immediately regret.

Anything classified as a fail is a possible "hold my beer" video clip.

b. (Twitter) An indication that, although events were awful, even worse calamities are about to present themselves.

2016: I've done my damage.
2017: Here. Hold my beer.
I can do THAT! Here, hold my beer!