Headsets
I don't have a problem with bluetooth headsets per se, I have a rather nice Jawbone myself, but rarely wear it outside the home/office environment.
The biggest problem with bluetooth, or even wired, headsets is the idiots who use them without realising that you DON'T have to hold the phone out in your hand while resisting the urge to hold it close to your mouth and with wired, you DON'T need to hold the mic while you're talking. The tw@t-o-meter goes off the scale when both these techniques are used simultaneously. It's called "hands-free" for a reason!
There's also a very strong argument for suggesting that the likelihood of someone using a headset in such a manner is inversely proportional to the importance of that person, but directly proportional to their self-inflated perceived sense of importance. See phone holsters strapped to the belt for details.