What is the meaning of the vernacular "beasted"?

I know Urban Dictionary is not usually a trusted source, but I think it is your friend here.

From number 2, here:

To have excelled at something as if using super-human beast like skills.

I heard this phrase used frequently whilst at university, but not so much since leaving. So I guess it's either a term particular to the student crowd, or to that particular area of the country.

It depends when it is used. When used on a performance, it means cool, super, excellent.

I beasted the exam!

When used on a guy, it can mean cool, or tank.

That guy is beast

However, when used on a girl, it means unattractive:

That girl is beast.

http://onlineslangdictionary.com/meaning-of/beasting-them

I think he meant "bested". Mysteriously, it means the same thing as "worsted"; to wit, "defeated".