A man who shaves small animals and fires the fucking thing up his ass using a tube of some sort. The animals can be any of the following: gerbils, mice, hamsters, rats (either sewer or store boughten), beavers, muskrats, small dogs, large dogs or pretty much any other animal you can think of shaving.
Look at the waythat guy is standing near the waterfalls. I would bet hes a serious gerbiler.
Gerbilling is an odd practice of inserting a small rodent (mouse, often) into a condom which is then inserted into the anal cavity, where the dying convulsions of the pooranimal are said to produce a pleasurable effect.
The term is derived from a combination of the two practices.
As heard on the train platform: "Get outta the way, you fudge packing gerbiller!"