Does all urine kill sperm?
Ben (age 19)
Urine is acidic and sperm is damaged by acids. Since only one tube is used for both urinating and ejaculating in a man, your body produces a fluid called pre-ejaculate or in current slang, pre-cum, that neutralizes the acid of any leftover urine in your penis and flushes it out of your urethra. This is why when you get sexually excited there is a wet spot on your pants near the end of your penis -- it is the pre-ejaculate coming out, which indicates your body is preparing for sexual intercourse. The same fluid is very slippery feeling and provides a small amount of lubrication during sexual intercourse.
I must admit, I'm puzzled why the word "all" appears in this question. I have a feeling that you have something mind that I probably missed. There is a myth floating around that if a girl urinates after sex she won't get pregnant. It is false because a woman's urethra is separate from her vagina. Her peeing won't flush out or destroy the sperm inside her. See "Getting (Too) Close" for several other myths that don't work.