HARD TO SWALLOW
There are more than 3 million bacteria per square inch inside the average toilet bowl. When you flush, those bad boys get ejected into the air and land on everything in the room, including that innocent bystander otherwise known as your toothbrush. Can you say "ick"? Always close the lid before flushing, and store your toothbrush in a drawer, advises Donna M. Duberg, M.S., assistant professor of clinical laboratory science at St. Louis University.
There's also this article that I found about putting down the toilet seat before flushing which includes a more scientific viewpoint. It's a bit long but very informative!
So, think you can do something as simple as putting the toilet seat down before flushing? Oh and you can also apologize to your "nagging" girlfriend/wife/mother/etc. for always telling you to do so in the first place! Looks like they had a point, after all.