you wait until they are gone...

have some consideration and find a time they aren't around....learn their schedule

I do it in the shower, or at night after he is asleep, or in the day when he is out with his friends.

As already mentioned by others, you either make sure you have the room to yourself, or do it in the bathroom. Simple as that.

get a fake spider (or real one if you like) and scare them outta the room when you want some privacy

very quiet under covers

Don't do it. Or use your imagination.

Have some self control or Go to the bathroom or wait till they are out of the room

This!