Usable as bot an adjective or noun, Pretendum refers specifically to adolescent girls who either dumb themselves down in general in order to impress a member of the opposite sex, or who on certain occasions, will just play dumb for attention from their peers.
Christine: She's so acting like Paris Hilton just to impress Greg!
Jacqui: Like, I know! What a pretendum bitch!
Christine: I hate how whenever they ask her to spell words in class that she just says the wrong thing on purpose and does that annoying little giggle thing afterwards!
Jacqui: Yeah, me too. I don't even know why she wants the attentions so bad...
Christine: I do, she's a fucking pretendum.