I hope that doesn't happen. Sounds more like me than him. I would probably try to focus on things that he is great at other than rollerblading to boost his confidence back up, since anything about rollerblading is probably going to remind him that he didn't live up to his own standards right now. Like if he was being sarcastic all the time, I'd talk to him about what a great sense of humor he has, instead of telling him how good he did in the competition. Even if he did great, if he honestly doesn't think so I doubt you'll be able to convince him. I have no idea if this is the best way to deal with it, but it's how I would. I know I tend to avoid conflict situations and that may be part of it, so take my advice with a grain of salt, I've never been in this situation.