When Onizuka's pant's caught fire, it burned the mark "Death", on his butt in kanji.
Urumi Kanzaki's left eye is "brown" but her right eye is "blue".
When Onizuka gets Mr. Teshigawara's name wrong for the 3rd time, there's the sign "Teshigawara" on his back when he walks away.
Murai stepped on a fermented soybean and got mad at Onizuka, as his face was zoomed in, you can see a mark in his forehead the word "kill" in kanji.
Somehow Eikichi was able to write Doraemon on his own forehead, with bowling balls glued to his fingers. He was even able to hold his cigarette like this.