Yes, there was one time a ticket agent (not a gate agent), made me lose my temper. About three years ago, I was traveling NRSA (Non-rev, Space Avail), w/ my family. I was about sixteen at the time, and my little brother was about thirteen. Well, my brother and I were wearing a short-sleeved shirt and shorts.
Well, when we checked-in at LGA, the ticket agent said, "You're not flying today because, when flying non-rev, you must wear a collared-shirt with pants and dress shoees." Huh? My mom, who was a pilot for over thirty years, had NO idea about that there even was a dress code. We had planned this trip for about three months, and we were going from LGA to PHL to LAX. Keep in mind that this was the 6am flight, and everything was closed. I yelled at her, "What the Hell? We were planning this trip for weeks, and there are finally enough seats on the airplane for us to go, and now you will not let us make the thirty minute connection to PHL? All the other flights to LAX from PHL are overbooked!"

Her response, "I'm sorry, but it is a company policy."

End of story? No. She then had another ticket agent come up. My mom asked, "Well, what can we do? Is there any place for them to change." (Keep in mind, this was in the middle of July). She answered, "Ma'am, are you asking if I will go into the bathroom with your son's and change them?"

We walked away, found another agent who actually had kids and knew what it was, and let us through.

But, had I been a full-paying passanger, I would have never flown US again.