Unless you have something in writing stating that he was going to pay you $xx.xx dollars for the work, you have no legal grounds to stand on, and at the same time neither does he.

I'd be pretty hesitant to go after a hundred bucks, will probably end up costing more than it's worth in the long run (time off from work, court costs and so on).

Nothing comes between bros faster than women or money, in that order of course, and sometimes at the same time.

Chalk it up as a lesson learned, I'm a firm believer in "What goes around, comes around in the end", he'll get his at some point.

If you're going to charge for the help, get it in writing and get the money up front, no pay no play. The days of the "handshake deal" are dead and gone, it's all part of the downward spiral of mankind (just take a look around).