I can't pick just one bad experience. All of them seem to tie each other.
Getting a really bad case of food poisoning two years ago. I was throwing up for about 4 hours in my dorm room, and then my twat of a roommate comes in from the gym and opens the window real wide - in January, in Boston. When I went to student health services, they told me I had to go to the emergency room, where for 8 hours I had a few large IV needles stuck into my arm as I passed in and out of consciousness.
When I was 16, I needed a pair of dress pants for an honors society ceremony at school, my mother tried to see if an old pair of my father's pants would fit me so she wouldn't need to buy me another pair. The pants she had looked like they had piss stains on them but she insisted I put them on and she'd wash them later. Only after I put them on did she realize that they were old masturbation stains. Needless to say, I was pretty horrified and my mother shelled out $20 for a new pair of pants.
A year ago, I was talking to a guy online and he wanted to meet, just to hang out. So, I take a bus from Boston to Plymouth, MA, only to find that this guy doesn't really want to "hang out." He left me at the bus station in Plymouth after the last bus left. I was broke and had to try to convince a friend on the phone two hours away that I was worth picking up and taking back home.
Sophomore year in college, I was asleep, but then that twat of a roommate comes in shit faced drunk from partying with a friend and turns on the lights. As I slowly become awake, I realized that they were both talking really loudly about how ugly, disgusting, and weird I am and how "bizarre" my real name is. I think after that point I wanted to beat the crap out of my roommate.