When that happens to me, I make sure to let the person on the other side of that conversation know where it's being held.
I flush repeatedly, turn on the water, and take out my phone and have very loud imaginary phone calls, or just cycle through the available ringtones at high volume.
Some people are still so low class that it doesn't even phase them.
Hmm, you can also try to pretend you have one on yourself and laugh joker-style looking up then talking to the ceiling, making sure the volume of your voice was uncomfortably loud and inappropriate for the setting you are in. Its not like that person can call you rude and it will give you some satisfaction that you have interrupted their call. Maybe they will self reflect at some point realizing how rude they are themselves. IDK.
