Can you get pregnant if some one ejaculates on top of your vagina and you don't wipe it off right away.?

Yes: Even before a man ejaculates, his body releases some sperm; so if you're banking on him "pulling out" in time, it doesn't always work. Also, the sperm on the outside are pretty single-minded in trying to find your eggs. If you don't want to get pregnant, using condoms every time and/or seeing your doctor for other types of birth control is a better strategy.