You can not get pregnant by getting sperm on your jeans.
Even if those jeans are so tight that elderly women can tell from three blocks away that you’re not wearing underwear.
What you actually need to be worried about is getting sperm in your genes…
Explanation for why you can not get pregnant by making a bad fashion choice:
There is no way for the sperm on your jeans to get into your vagina, climb up through your cervix, and fertilize a fashion-forward egg. In fact, although the moisture from the semen might seep through the fabric of your jeans to get onto your skin, it’s not even terribly likely that the sperm would go with it. There’s a far better chance that the whole mess would dry into a nice crusty stain. Don’t worry though. Even if the dried semen gets onto your underwear while you’re washing it, you still won’t get pregnant.