Ready for another surprise? Males can be allergic to their own semen.
It's extremely rare, but it happens. Called Postorgasmic Illness Syndrome (POIS), it causes flu-like symptoms immediately after ejaculation, and (in some cases) cognitive symptoms that can last as long as a week.
"If you exhibit flu-like symptoms immediately after ejaculation, it's possible you may be allergic to your own semen, according to a  article by Reuters in the Times. ... In one study, 33 Dutch men who were diagnosed with POIS were given a skin-prick test with a diluted form of the their own semen - a standard allergy test."
Now, that would be a true problem.