Unfortunately I think, taken at random, 9/10 people fall into this category for me. On occasion, such as taking a sierra club group trip, you can up the number of annoying people to half a dozen.
I'm kind of a solo backpacker, but don't mind at all going with a few people who don't annoy me. I find certain features of people personalities that normally don't bother me, such as being very loud, and or whiners get to me when backpacking. During one group trip I did there was one guy I didn't know who talked loudly and constantly for 5 day straight about things like his daughters college applications and other detritus from the "real world". That REALLY got on my nerves and I took to hiking a far away from him as possible, but I still felt guilty about it since there was no objective reason for me to complain.
I always say choose your traveling and backpacking companions carefully. Very small things can annoy under certain circumstances where your idea and theirs of what makes a good tip conflict, and short of splitting up there can be no solution.