Lateral Thinking

[TheIrishThug]

Heard someone read this while in barnes and noble. didn't have time to think about it cause they went straight onto the answer. but knowing the answer i'm not sure if i would have been able to make the correct conclusion. so i'll let u guys give it a shot. if u've heard it before that doesn't count, i'm trying to see if ppl can do it.

here it is:
a guy walks into a bar and asks for a glass of water. the bartender pulls out a shotgun and says "get out of my bar." the man says "thank you" and leaves.
why does the man say thank you?