To ride or stunt on 50cc pit bikes or dirt bikes, usually in a group of two or more. Also includes 50cc go-karts, lawn mowers, weed wackers, etc. Mobbin implies that the riders are riding derty.
Dude let's go mob 50's on the trail dawg.

Shit, he fuckin ramped that siq jump. MOBBIN 50s!!!
by ryde50sdawg April 1, 2010
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