Bathroom Luxuries
My apartment does not have a toilet paper holder built in its bathroom. I feel like that is one of the most convenient items that a bathroom can have and it's such a simple install. At least I don't have to complain about guests leaving an empty roll on the toilet paper holder? Or even worse, when someone installs the toilet paper in the wrong direction! (You better choose wisely!) Think positively.
I can't stand bathrooms that don't have vents in them; luckily for me, my bathroom does. Vents are extremely important to exhaust the terrible smells and keep moisture under control (to prevent mold). But one of the most critical aspects of a bathroom vent/fan is the noise. It probably means someone if occupying the bathroom or it stinks in there. And the noise will mask the natural (and unnatural) sounds human bodies make while during regular bathroom activities from anyone nearby.

I wish I had a heat lamp especially since the winter is coming. I wish could eliminate any exposure to the cold air. Drying off after a shower with music and walking out to the warmth of the heat lamp then put on my Jedi Bath Robe. That would be the ultimate experience to end every evening.
The heat lamp would be pure luxury. Other bathroom luxuries I would want: Heated floors, heated toilet (not sure about a toilet that cleans by shooting water), anti-fog self-cleaning mirrors, maybe a television, but most desired luxury, a method to clean up facial hair completely without much effort.
P.S. The most irritating aspect about a bathroom may be if the water faucet is too close to the sink walls.