Walking giggles

OK, a new post has been requested. Till I get a real one, here's what happened the other week when I was out on a walk:

[As Sharon walks past guy biking who stopped to take a drink...]

Guy: Hi, want a drink?
Sharon: No thank you.
Guy: I have clean lips, believe it or not.
Sharon: I believe you.

[... keeps walking, finally gets far enough to laugh convulsively]