In high school, this (straight male) troper was so close with my best friend that I occasionally had to explain HeIsNotMyBoyfriend, although we were both amused rather than annoyed. Several years later, I found myself on the receiving end of an annoyed "You're not my boyfriend!" from the same friend (long story, ItMakesSenseInContext), said in the same tone as "Don't tell me what to do! You're not my mother!"

I work at a butcher's and minor injuries do happen occasionally. However, it's sometimes hard to tell whether someone is bleeding or just has animal blood on their hands. My boss stabbed himself with a brining pump, and noticing he was bleeding everywhere I said "Is that YOUR blood or just animal blood?" A few months later I take a minor injury to the knuckle and start bleeding. My boss, noticing the lack of visible injury (it was just a chip out of my knuckle) said "Are you sure that's your blood and not blood from an animal?"

A heartwarming variant occurred between my brother and I. Once, my brother and father got into a shouting battle and my dad called him a dick. I told him coolly, "Don't call him that." A few months later, a bully and I were having the same kind of argument, and he told me I was a bitch. Cue brother.

For this tropette, once a certain guy in her class called her "a clumsy bitch." Later on when he fell, I said to him, "You're a clumsy bitch." The look on his face was priceless. (BTW, this sort of stuff happens a lot, so in reality we're actually VitriolicBestBuds)

Two examples from this Troper's life, both from "primary" (see European School's system if details are needed):

The first one is a mix of Echo and IGotBetter. Back in first grade Primary, I was one of the worst in my class at learning languages, to the point of me having to have an extra teacher with me to english classes because I wouldn't understand a ''word'' otherwise. Nowadays, all of my four languages (Swedish, English, German and Latin) are the subjects that I have the highest grades in. It was even echoed twice: when a new guy came from Sweden (where the education is admittedly not as good as this one), he was - sorry, pal, if you ever read this - not good at all in english. The person who earlier needed an extra teacher herself got to be his half-teacher, half-fellow student!

My extra teacher also was responsible for me getting used to life at school, and told me: "You're not at a café in schooltime, try to sit normally without crossing your legs like that!". Cut to Secondary, where I visit the school cafeteria almost every Wednesday (I have a permanent free hour then). And I'm sitting normally.

This troper considers it practically a hobby. Woe to the person who lays upon him an unwarranted insult or stupid platitude-chances are that insult will come back to you within the month. Or in some cases, within the minute.