I always strike up a conversation while on a public toilet.
If I walk in the restroom and someone is on the jon, stinking up the place, I'll say "Wholy heck, how about a courtesy flush!"
If I'm sitting on the toilet and someone occupies the stall next to me, then I'll start singing something like "Mary Had A Little Lamb" or some other nursey song. If I let out a loud one, then I'll say "OMG, that sure felt good, but wet."
LMAO, this one guy came in and sat in the stall next to me and had the most foul smelling number two. I said "Dang dude, what you been eating?" He didn't say anything but I could hear him trying not to laugh.
The best thing, though, is to turn out the lights when you exit, leaving whomever sitting there in the dark.