Buying drinks can also be seen as someone weaker (financially) asking someone stronger. Considering that men earn more on average than women, and if you are picking up college girls and have a real job that is likely to be even more the case. So I don't see the way that these situations can be easily distinguished that way by someone without much social experience

I have a few meta-rules of thumb in such matters:

1. Anything can mean anything.

2. Corollary: Never explain by malice that which is adequately explained by intelligence.

3. The rules are never what anyone says they are.

4. The rules may not even be what anyone thinks they are.

5. Nevertheless, there are rules.

6. It is your job to learn them, and nobody's job to teach them to you.

7. All advice, however universally it may be expressed, is correct only in some specific context.

Application of the last to the whole is left as an exercise. :-)