Actually, it's not the worst, but it's bruised me enough that I still have bitter memories. First semester of college (several years ago), I met a guy who was in a relationship at a dumb Halloween party. This story has a lot of details, but I'll try to streamline so as not to bore people with an even longer post. As it turns out, not long after he met me, his girlfriend dumped him. I had no strong interest in going after him, but through a series of events, I ended up becoming his rebound/shoulder to cry on for 2-3 months. Unless he was totally screwing with me, which I have a hard time believing, there was some kind of spark; we cuddled in front of people, spent time alone in my room (lying in my bed once or twice), etc. He asked me to hang out over winter break. He comforted me when I broke down crying. A decent amount of people in our mutual group (the girls on my floor and handful of guys from other floors were pretty tight) knew that I had, at least, had started crushing on him.
He came knocking on my door when classes started again, which he had done often enough before that people were used to it. Then...he dropped off the radar. Boom. Even my roommate worked up the gumption to ask. I had a sinking feeling that I knew what was happening, but was too much of a coward to confront him. Part of me held out hope, although I also wasn't going to force myself on someone who didn't want me. He ended up going after a girl who lived a couple doors down for me, without ever having the guts to tell me that he made a mistake about his feelings. Seeing them everywhere was so awkward, and eventually one of his friends cracked and told me they were official. I think he pitied me. It was really embarrassing to feel like everyone thought of me like that. Soon afterward, I spent as little time as possible in the dorm.
I was naive then. Looking back, my behavior was natural based on my childhood and high school experiences, but I wish I was less clingy or, I dunno, awkward in certain respects. If this happened now, I would also keep more distance even if I let someone open up to me about relationship woes. Bottom lie: I'm not writing this to throw a tantrum. I don't regret anything from the experience—except how he chose to end it. He knew how inexperienced I was, and it would't have killed him to be nicer. I truly felt like dirt for ages.