Youtube Sensation 

A euphemism for someone who doesn't realise that the skill they are showing off is only considered remarkable by other people because of how embarrassing it is.

A: So...saw Jack dancing last night.
B: Jack was actually dancing? Does a guy that big have moves?
A: Ummm, how to put this nicely....lets just say that if someone was filming then that guy would be the next Youtube sensation.
B: That bad, huh?
A: Think Star Wars Kid, but with less coordination and more sweat.

Youtube Sensation by WhiteLando June 4, 2014

Instant Youtube Sensation 

Any Youtube video that has achieved:
1. Millions of hits instantaneously.
2. A cult following or numerous parodies on other televised media.
3. Provoked numerous responses or imitations in a short amount of time.

Common examples of instant Youtube sensations include the Star Wars kid, Crazy frog, Cadbury gorilla and recent eyebrow advert, Sarah Silverman's "fucked Matt Damon" sketch, etcetera. Basically any video that matches the definition.

Instant Youtube Sensation by Firelovesugar March 18, 2009