It's not that she walked in on me in the bathroom that was the real problem. It was the fact she came back for a second time to tell me that this happens to her, "..all the time."
"So many times," she continued, that she'd actually "lost count." I reassured her that she wouldn't have to wait long, but that she would have to wait outside the bathroom.
She was gone by the time I'd washed my hands and left the Ladies to return to the dining table. I saw her, mid-squat, telling her friends what I assumed was the story of her walking in on me sitting on the toilet. I assume this because of her exaggerated, animated gestures and scrunched-up face. Her friends were mesmerised by her retelling.
I took a detour on my way back to my table, and went over to hers, putting an arm around her hunched, crouched body - startling her out of her caricature - and said "I'm sure my face didn't look like *that* - I was only peeing."