Regarding airport bathrooms:
I have a feeling I'll regret disclosing my airport bathroom secret, but whatever:
Find the "Family" restroom.
Every airport has several of them, and they are completely private. Look for the non-descript door located near the general restrooms. It is a one-holer-bathroom with a lockable door that is almost always available.
For those interested, this is the best place in an airport to smoke your cigarettes, or whatever *ahem*.
Just make sure you're prepared for the shame that comes with leaving a smoke filled "Reserved For Families" restroom, when there is a family waiting right outside as you leave.
Ryan