More UA stupidity at its finest.

There is no such rule requiring gate checks for flights to DCA - that response was nonsense.

There is no such rule requiring the use of a rear lav on flights inbound to DCA - that response was nonsense. There is a rule requiring all DCA pax to be seated while the seatbelt sign is illuminated, but you were simply a double-victim of UA employee security paranoia and misinformation.

Don't bother writing in - they will just send you some boilerplate nonsense about not discussing security matters and how much they value your safety and support the vital mission of the TSA. You'd almost want to vomit reading it.