I made fun of a few people (behind their backs) who did not deserve it when I was younger and stupider. Still weighs on me, considering how much I myself was made fun of.
I still make fun of people today, though they've usually done something to deserve it (mostly celebrities, ignorant politicians, and people who are being jerks). Though of course, they never see or hear anything I might say (unless the jerk in question is online or something). For the most part I hate mockery and try hard not to be malicious unless somebody else is malicious first. I don't make a habit of it, but if somebody dishes it I feel they should take it.
I make fun of myself all the time. Sometimes it helps get me through embarrassing situations, if I can deliberately make others laugh at me rather than accidentally make them laugh at me.
I came from an anxiety forum before this one, a site where MANY users had been mercilessly bullied and ridiculed much of their lives, and, sad to say, it's often the people who are frequently mocked who most frequently mock others...if that makes any sense. And most of them saw not a thing wrong with what they were doing, even while they still complained about the treatment they received from others. I'd always thought being on the receiving end of mockery made one more sensitive to the feelings of others, but often it's exactly the opposite.