What constitutes "creepy" in social interactions?

This question has me thinking about what sorts of social interactions are considered “creepy” by women. To me, if a guy working in a coffee shop that I frequent on regular basis, told me that I had a nice smile or beautiful eyes, I would think he’s charming. If he said he found me attractive and asked me out, without having much in the way of conversation with me, I would think he was forward. If he persisted in asking me out after I said no, I would find him creepy and probably change coffee shops.

However, any number of younger women that I’ve encountered seem to find the act of complimenting eyes, smile, appearance to be a creepy overture, or unwelcome attention. What’s the line between a compliment or conversation starter and being hit on? However are guys supposed to know what to do?