Miley Cyrus -- Snatches Beer in High-Risk Move

Miley Cyrus has become a real risk taker lately, but the one she took Thursday night with a stranger's cup of beer is insane.

Miley was singing something -- it's hard to tell which song -- when she got thirsty and spotted someone in the audience with a cold one.

It appears to be a stranger ... but ever the daredevil, she took a swig.

Now we're not trying to be alarmists, but seriously Miley ... do you know the history of the mouth that drank from the beer before you?

Actually ... the real question is whether the guy finished the beer after Miley gave it back.

Fun Fact: You can get herpes from sharing a drink.