I agree... Have you ever noticed how tae kwon do sounds suspiciously like "take one's dough"? *cough* In most of the American schools (not all, but at least all the ones in my experience. I took 5 years of TKD myself), you just pay for your belts. We have two taekwondo guys that come to my Brazilian martial arts academy, and they get their butts handed to them every day. (We do Capoeira, Brazilian Jiu-Jitsu and a little MMA there.)
Back to the original post, though. Where do you work? I cant think of many jobs, outside of maybe night-clubs and blue-collar jobs, where the coworkers will actually beat someone up for standing up for themselves. I mean, how mature are these people? Seriously...
Either way, yes, a martial art is a fantastic way to boost your confidence and give you the security to be able to stand up for yourself, and protect yourself if they really do decide to get after you. I recommend taking a Brazilian jiu-jitsu class or two, as well, since unless you can successfully take someone out on the feet every time, the fight will probably end up on the ground sooner or later. If you know even a little BJJ, you've got a huge advantage over someone with no knowledge. The beauty of BJJ is that smaller, weaker people can beat much larger people if they know what theyre doing.
(And if you can choke someone unconscious, rather than breaking their leg or something, you'll be better off legally, as well.)