Jumping over a bunch of stuff riding a mountain bike is a lot of fun. You know what's a lot more fun? Jumping over a bunch of stuff riding a mountain bike while some dude spits fire all over you! [Thanks Karl!]
The potential problem I see with this is that spitting fire isn't just spitting fire, it's spitting flammable liquid that just happens to be on fire. That's liquid that could easily land on something and continue to burn.
I imagine the after picture is this biker covered in grass stains with partially burned clothing.