A combination of "skinny
" and "attitude
"; the loud, boisterous, obnoxious arrogance often displayed by skinny "beautiful people" with low to no intelligence and/or small sexual attributes such as breasts or penises'. This is very common; many thin people often try to compensate for their insecurity with their mental and/or sexual triviality by loudly and cruelly berating "overweight" people.
"oh no he didn't just say that, that skinny ass moron on this talk show better just get over his tiny penis and own up to his skinnitude"
A word fat kids use to describe people who bullied them at school.
Fat guy: Oh man Terry has pretty a bad skinnitude, he keeps calling me fat
Normal guy: Terry is right, you are fat!