if the tip of the penis brushed against the toilet seat, what are the chances of getting ANYTHING
No way you have a problem. The CDC says you can't catch either of those bacterial infections from inanimate objects in normal social contact. You can get them if you share sex toys, but not from the toilet seat, or the office equipment. Think of the mechanics. Both those diseases need to get into your bloodstream or urinating "plumbing." So, let's say some chlamydia or gonorhea infected "smootz" gets left behind on the toilet seat or office equipment (that would be really gross since she would have to be masturbating with pens and pencils). Unless, you rub your privates right on the toilet seat or use the pens and pencils right after her for the same masturbatory purposes the only place you'll get the infected "smootz" is on your skin. Unless you have cuts or abrasions skin is a very good barrier to every STD except for mucous membranes and well I have never seen mucuos membranes on the backs of your thighs.
I don't believe you have anything to worry about, but good luck anyway.
i doubt it....germs die pretty fast when they hit the air.....but to be sure keep ur booty raised above seat and make sure aim is good or use Clorox wipes!:))))))