I think if you are brandishing it in order to intimidate, then you're threatening to use it offensively instead of defensively. IMO, that is highly irresponsible and I would imagine doesn't represent the majority of legal gun owners. In this specific case, the guy in the pickup has a clear advantage over the armed rider, and that only makes me think the rider is an even bigger moron. I used to belong to a few motorcycle forums, and it would be hard to find anyone more irritating than a gun-toting "squid" (aka douchebag on a bike) anonymously flexing his internet bravado. We can only hope that he will eventually remove himself from the gene pool before he can hurt anyone else.
Oh, and if this guy's motorcycle can't even blow past some guy in a pickup before he even has a chance to get angry, then his motorcycle sucks too. You can C&P me if you'd like.