I have 2....and they are 2 different reasons!
1) Vortex...it was my first real big coaster, first upside down coaster. I will never forget them asking for 2 riders and them giving us the front seat. I thought I was riding with some one who had been on it before, we got to the top of the ride and my friend goes "Cortney, I've never been on this before!" and we screamed the whole way down that first hill!! I haven't looked back on coasters since.
2) Nighthawk at Carowinds. The first time I rode it, and I will probably never get back on it. But I thought for sure it would be like Firehawk at Kings Island, got on there and looked around and found you had ZILCH to hang onto and that freaked me out a little bit. To top that off, we were in the front row and also the ride operator going "It doesn't matter where you are riding, you see the water the same way!" The ride up the hill I kept asking my aunt "Are we at the top yet?" She was like I'm not telling you, I begged her to hold my hand, and she wouldn't. The second we flipped over, it was like a rush of emotions. I was scared, I was happy, I was crying, I was screaming....you name it! LOL It was well worth the 1.5 hour wait, but I doubt I will get on it again. It was too much for me.