Simple Math

Put it down. As much as I will defend guys at nearly every turn, this is a no-brainer. You put the seat down.

Look at it like this: Every person has two sorts of jobs to do in the toilet. For the sake of cuteness we'll call it the Little Job and the Big Job. Men do the Little Job standing up, though they could do it sitting if they wanted to do it that way. They do the Big Job sitting down.

Women do the Big Job sitting down, of course, but also have to do the Little Job sitting down. It would not be wise for a woman to attempt the Little Job standing up.

Now, in a two-person household that includes one man and one woman, that gives a three in four chance that whatever job is being done in the bathroom right now is a sit-down job. You can add additional males all you like and the math still comes out in favor of keeping the seat down. Male child joins the household? You still have a 4-to-2 ratio going that the job is a sitter. Two sons? 5-to-3. The math will always come out this way. And as superior as men are in math, with their bigger brain and all that, I would think this is pretty clear.