Guess it depends on the person. Some people are very sensitive around certain issues I guess. If it's something central to your life and identity though- and you feel like people are always taking pop shots at it- probably any small thing will just compound how ostracized you feel. I think some people have genuine grievances because their 'kind' have been shunned or picked on likely throughout their lives. So- if it's some snide remark about gender, race, appearance, sexual orientation etc- they may just snap because they're sick of hearing it.
If it's just a phrase they don't particularly like though- I imagine people could just be asked not to use it. I imagine the more extreme response of being offended is because there was something they found offensive about it. If they're actually a friend- it's probably worth finding out what upset them.
