My new least favourite adaptation of a word is the use by the younger generation of the word "onto".
For example...
"Mum, what is a cat?"
"It is a four legged animal, often domesticated and related to other cats of the feline species"
"Ah, k, onto"
Which roughly translated means "I understand what you have said, so thankyou for explaining".
I witnessed an exchange between my niece and some of her friends on facebook when the Breast Cancer "post in your status where you put your handbag when you come home but pretend like its something a lot ruder you are referring to" thing was doing the rounds, where they were discussing one of their parents updating their facebook status with the appropriate hangbag related comment with a mildly smutty context - and one of them thought that the mother was just in fact posting things that a mother shouldnt post on her facebook status - and really didnt get it at all - and the jolly chums were all mocking him and telling him he really wasnt "onto".
About 15 of them, all ending a sentence with "you arent onto". Terrifying.
I quite like Prolly though, mostly because I am fundamentally lazy.