Oh snap!

This meme (as YTMND says) came from two sources. One was a song by Biz Markie involving this catchphrase in his rap parody "Just A Friend". Another was a commercial of VW (Volkswagen) GTi series cars. In the commercial you can see a German speaking with native accent, getting 'unpimping ze ride' (which basically stands for destroying a tuned car). Thanks to these two main variations it became a really well known meme.

Rap parody:
https://www.youtube.com/watch?v=jSDXcpXJr4M

VW Commercial:
https://www.youtube.com/watch?v=-y_J77RO-wY

"Oh snap!" catchphrase is an indication of surprise or can be used to follow an insult. Usually used in image macro, etc.

It's really hard to tell when this started to evolve, but a lot of people used this macro, even College Humour in their "We didn't start the flame war":
http://www.collegehumor.com/video:1907543

Short, but useful, "oh snap!" is about 5 years old