that...... stinks

Did she just stand there and watch? Or maybe she offered encouragement? I'm not sure how important your friend's brother's girlfriend is in your life, unless she was videoing the encounter and posting it on OnlyFans.

And if they had told you, what would you have done differently? Waited an hour until you got home? Posted someone outside the door to stand guard?

Life lesson—only take dumps on your own territory!

If the lock didn't work, then everyone should know to knock before just barging in. Plus, a closed bathroom door usually means someone is inside. Not your fault she's too dumb to realize that.

Am I the only person in the world who knows to knock on a closed bathroom door?

I will never understand anyone who doesn't knock when the damn bathroom door is closed?