Sick

For me, the slang meaning of the word sick has always been "disgusting".

In current adolescent parlance, the meaning of the word sick is something along the lines of "awesome"

About 80% of the time, this is fine. I'm familiar with the new meaning, even though it isn't part of my active vocabulary, and you can usually tell by context.

The problem is those few times when you can't tell by context. This happens especially often on the internet, particularly when the word is being used by someone a bit younger than me, who would likely have both meanings in their active vocabulary. (I don't know whether or not Kids Today use sick to mean disgusting, but I doubt someone 3-5 years younger than me would be unfamiliar with the that meaning.) If someone says, without elaboration, in response to something like a dirty joke "OMG, that's SICK!" it could really go either way.