"I can't wait" can't be used literally?
In general, "I can't wait" means being excited about what is happening soon, However I
wonder as a non-native speaker if it means I can't wait literally(maybe busy or in a hurry, something like that)

What do you think about that?

Question

"I can't wait" can't be used literally?
In general, "I can't wait" means being excited about what is happening soon, However I
wonder as a non-native speaker if it means I can't wait literally(maybe busy or in a hurry, something like that)

What do you think about that?

Answer

I agree with Gary and Greg. You can use the expression both ways.

Answer

Yes, it's used a lot to say you're in a hurry and need to go.
For politeness, you often qualify it by apologizing or giving a reason. "Sorry, I can't stay, but I have to go for an appointment", "I can't stay - I need to be at the college in  30 minutes".

Answer

Yes, it certainly can. 
You would need context to work out the meaning. Usually in the second case, you would also use something to make it more polite, as it sounds a little rude on its own.
It's your birthday next week, isn't it? / Yes, I can't wait.
(In a queue) Do you mind if my son uses the toilet before you? / No, sorry, I can't wait.