My best friend asked me out on a date but...?

I think he might be taking it seriously, but he's worried about how you'll react. And so that's why is kind of jokingly, but kind of not. He probably doesnt want you to get angry or something because he doesnt want to lose your guys' friendship. Go out on the date, but whatever happens, don't lose your friendship with him though. If it doesnt work as a relationship, just go back to being best friends. Just say, "Listen, I don't think this relationship is working very well, but I like you alot, and i want to go back to being friends."