If you are in a dining establishment and need to.
Today's topic is bathroom etiquette, and we'll begin today with public bathrooms.
Proper Bathroom Etiquette
If you are in a dining establishment and need to use the lavatory, try to wait for a good moment (say, just after ordering) to excuse yourself so your fellow diners don't feel awkward waiting for you if the food arrives. Some restaurants have separate men's and women's bathrooms, while others have coed restrooms. If you are using a coed bathroom (especially if you are a man) remember that others will have to use the toilet after you. Men, make sure to lift the toilet seat before urinating; if you are concerned about the sanitary conditions, you can use your foot to gently lift the side of the toilet seat up or down. You also may use some toilet paper, tissues or paper towels to move the seat. And men should lower the seat after they are finished. If there are separate men's and women's restrooms, then I think men should feel comfortable leaving the seat up when the restroom is busy and stalls must be used as urinals.
Public Bathroom Etiquette
For public restrooms where an attendant is present (less common in the US these days, but still seen in some fancier establishments), the attendant will hand you a towel after you wash your hands, and may also start and stop the water for you. There will usually be gum, mints, and hair gel available, which you may use. It is customary to tip the attendant if they have provided some service or supply; usually a dollar. In some countries, many public restrooms have attendants and it is customary to leave a small tip in the tip dish.
When it comes to the debate between men and women about whether to leave the toilet seat up or down, the answer for everyone is to leave both the toilet seat and cover down.