Is there a rule anywhere that says a unisex lav. can't be used by someone without special needs (e.g. someone disabled, with a baby, etc.)? If not, it seems to be the FA in question was guilty of being inconsiderate by spending so much time in there but not anything beyond that (I can imagine that those types of washrooms appeal to persons needing to change clothes for whatever reason, so maybe that's what was going on). I think it would be a waste of time to write UAL WHQ about your sense of outrage unless doing so would make you feel better.

My personal view is that the unisex facilities should be treated like the "priority seating" seats on busses -- anybody can use them until someone with special needs comes along, at which point their use takes priority or they go to the front of the line if other people are waiting. I'm sure others would argue that there shouldn't be preferences at all, and that those with special needs should feel fortunate to have a place that accommodates them but that they shouldn't get any faster access to it. I've been at football games where someone in a wheelchair has come in needing to use the wheelchair stall, but the person has waited in line with everybody else...