“You know, I'd love to, but I can't.”

Your coworker invited you to go out for drinks after work today. You don't want to go, but you want to be polite so you say:

You know, I'd love to, but I can't.

You know,

"You know," is a way to start a sentence in spoken English that can make the sentence sound like you're going to say something new and interesting. In the example above, the phrase "I'd love to, but I can't" is a really standard, boring phrase. So adding "You know," on the beginning makes it seem a little more interesting and friendlier-sounding.

I'd love to (do something)

Use "I'd love to ___" when someone invites you to do something. The phrase shows that you're excited about it and you want to do it. Here are some examples:

I'd love to join you guys, if you don't mind.

A: Do you want to get together and have a drink some time?

B: I'd love to!

I'd love to, but I can't.

This is a polite and extremely common way to say "no" to an invitation. When someone invites you to do something, but you're busy at that time or don't want to do it, say this phrase and then give a reason:

I'd love to, but I can't. I'm completely broke this week.

I'd love to, but I can't. I have a karate class this evening.