lol, i suppose! casual in japanese is MUCH harder than polite! i've studied for 6 years now, and had to think about how you'd say that casually. The thing about casual speech is that it eliminates all the particles that tell you things. Also, casual is sorta abbreviations.

sono kata zenzen dame da yo -- 'that thing/way is totally wrong'
hontou ni zettai chigatta - 'honestly that's just wrong'

anything else?