There are some things that, at my advanced age, I have managed to figure out. One thing I know about myself is that I think, nay, I know, that public restrooms are scary and gross, always. Even the ones that look clean still have incipient germies that are just waiting to leap onto my privates and have a party. I know this, with every single molecule of my being, and will not be talked out of it by "scientific studies" that "prove" otherwise.
So my fail-safe drunk-o-meter is: peeing. I can tell how drunk I am by just thinking about going to the bathroom. If the idea of putting my delicate bare bottom directly onto a toilet seat seems reasonable, I need to stop drinking immediately.
If I'm sober or close to it, I follow my usual routine of cringing into a stall, pulling off the top few sheets of toilet paper and tossing them into the toilet (they are contaminated with invisible toilet-flushing germy spray), pull off a "clean" wad of toilet paper, and hover above the toilet seat while making sure none of my clothing is touching any part of the toilet base. Upon exiting the stall, I wash my hands, then open the bathroom door with a paper towel. If the restroom was spectacularly gross, like in a rest stop or a convenience store, I then follow up with some hand sanitizer.
If I am buzzy but not drunk, I will loop happily into the restroom, hover above the seat while hanging onto the stall door, wash my hands and not worry too much about touching the door handle on the way out. If I am drunk, I'll plop my butt right down onto the seat. I'll flush the toilet -- hopefully I'll remember to flush the toilet -- with my hand instead of my foot. I'll most likely primp a bit in front of the mirror and then bounce out the door, completely forgetting to wash my hands.
One terrible, awful, very bad night saw me staggering into the bathroom, peeing on myself slightly when I couldn't fumble open my pants fast enough, tipping sideways off the toilet seat (because of the spinning restroom, you know), staggering directly back out into the bar without stopping at the sink or even glancing in the mirror (whether or not I flushed remains a mystery).
So now, after I have one drink, I'll do a systems status check: would I sit on a toilet seat? If the answer is no, I might have one more drink. If the answer is yes, alarm klaxons go off in my head that send me looking for a bottle of water and something solid to eat, like an entire loaf of bread, maybe.