Went through a Jack in the Box drive-thru today, which I haven't been to probably in ...20 years (at least since their e.coli scandal years and years and years ago), so I needed slightly more time than normal to figure out what I wanted, and asked the drive-thru worker for more time when she came on the speaker.
Me: "Can I have a couple minutes to look at the menu?"
Her: "Sure. Let me know when you're ready."
Me: "Thank you!"
Her: *mocking tone of voice* "Thank you"
EDIT: What I mean by mocking tone is that same tone that little children use when they're making fun of something someone says. I have a fairly high-pitched voice, and the drive-thru worker DIDN'T, so when I heard "*squeaky voice* Thank you" back, I knew she was making fun of me. If she had just replied with "Thank you" in the same voice she had, I wouldn't have cared at all.
Me: O _O?
My husband asked me what the fuck that was, and I said, "I think she didn't realize the speaker was still on." He told me to just leave and we went elsewhere.
That's what I get for being polite.