Jealousy: Exhibited when he and Kamui made their promise. Kamui first makes it to Kotori, leaving Fuuma completely out of the picture. (his promise being, I believe, that someday he will wed her) You have to look closely, but you can see that Fuuma is jealous, he immediately promises that he in return with protect Kamui (and Kotori as well)- Kamui is forced to acknowledge Fuuma and promises back that he will protect him as well.

Insanity: A few panels in the first few manga of X (2 or 3 I believe) depict a dream Kotori's is having wherein their mother has just died in the operating room. The dream flashes back to her and Fuuma finding their mother - who has just birthed the shinken, and thus is a bloody mess - Fuuma (in a gesture totally inappropriate for the completely sane) dips a few fingers into the blood and proceeds to lick it and smear a bit on his face.

;P I think I'm the only person in the world who actually paid attention to Dork!Fuuma, and thus, read those manga in detail. But I can't help it! Fuuma and Subaru are my favorite characters. :/