stating the obvious

[waider]

Sheila: Can I get some water, please?
Waitress: certainly

waitress returns with water and two glasses with ice in them.

Sheila: Oh, I didn't want ice.
Waitress: How about you, sir?
Waider: Uh, no, I'm cool.

waitress and Sheila burst out laughing.

Waider: (slightly bewildered) What? Oh. Right.

That's what I get for using "I'm cool" or "I'm good" as a synonym for "no thanks".