I grew up in a home in which any kind of teasing behavior was not acceptable, so my default inclination is to be offended by anything that sounds like teasing. In larger society, however, this reaction is often not appropriate, and I could waste a lot of time and energy rushing to the defense of people who neither need nor want defending.
Since I am ill-fitted by both nature and nurture to differentiate between good-natured teasing and the more sinister forms, I try to gauge the reaction of the person targeted by the teasing to make that determination. If the targeted person seems to be amused by it, I know that it's not worth getting upset over. On the other hand, if the targeted person seems to be upset or offended, I know that it's not okay with them. If it's not okay with them, it's not okay with me, and no amount of rationalization is going to make it okay.
Maybe this is not an ideal system, but the alternative is me flying off the handle over every little thing; I certainly don't want that, and I don't think anybody else does either.