Today I cycled over to see a friend who's just got a new bike but was too nervous to go out by herself on it - we'd arranged to go for an easy cycle near her house on cycle paths.
It's about 30 minutes to her house from mine, I'm currently pregnant and I'm pretty sure my baby thinks my bladder is a trampoline
When I arrived she opened the door, but held it half open and sort of stuck her head around it to talk to me. I handed over some stuff I'd brought for her and asked if I could use her loo, saying it was ok if I couldn't (I guessed from the way she was holding the door that she wasn't going to ask me in), I'd go up to the coffee shop a few streets away.
She said sorry, no, the house was a tip, so I went to the coffee shop and came back. We went for our cycle and it was all good, then I went home again afterwards.
It's probably me being unreasonable but I was a bit put out, though obviously I didn't let on to her that I was. If a friend asks to use my bathroom, I can't imagine saying no, I would feel rude if I did. (Though I have on occasion said 'yes, just let me run up and check it first' then done a quick removal of laundry on landing / emptied the bathroom bin).
It was still bugging me a little so I thought I'd ask options here as to any etiquette involved. Typing it all out has done wonders though and I'm no longer bugged
It may have been more of a friendship issue than an etiquette issue.