Vanessa Hudgens -- My Ass is Small But I'm Twerking Like It's BIG

What's good for the Miley is good for Vanessa Hudgens -- and GREAT for us to watch ... because the former Disney star opened up her own twerking clinic last night.

Vanessa performed with her new girl group YLA at Bootsy Bellows -- doing some singing, some dancing ... and then tried like Hell to shake her ass right out of her booty shorts.

Here's the thing ... Miley Cyrus caught major flack for displaying a lack of back during her VMA twerkfest. Does Vanessa's ass action deserve the same ... or does it get a pass?