......... I have the same problem sometimes. Although I only know "greasy" to mean "oily", as in having greasy hair, so it's really oily and sticky.

Cheesy ... it would be something really sweet and romantic, but the kind of romantic gesture that makes you kind of know is grossly exaggerated, even though it's heartfelt. So like ... saying "I would wish on the brightest star for the most perfect person to be by my side ... but I already have you." So I would mean "you are amazing", but I'd be saying it in a really sweet and "cheesy" way.

Corny ... I think that's kind of like a joke. Something that's really bad, but also pretty funny, and usually pun-based or is based on another form of word play. Like "French people eat snails because they don't like fast food." because snails are slow, or "I used to be addicted to soap, but now I'm clean."

Corny and cheesy are interchangeable. So a "cheesy" chat up line can also be a "corny" chat up line, and a joke that is corny can also be cheesy. That's how I use them here, anyway.