Judging from the number of users I see experiencing pregnancy scares on the Scarleteen message boards, particularly from situations besides genital intercourse, you’d think sperm cells were some magical weapon of mass fertilization, powerfully wiggling their way through clothes/towels/fabric, and leaping off hands to impregnate every person around them within a 50 mile radius. Look out for scary sperm! Get outta the way! They're coming right for you! (pun intended)
As a volunteer for Scarleteen, I'm here to tell you none of this is physically possible. It just isn't. As a former laboratory technician at a fertility clinic, having worked directly with sperm and semen (and without having ever gotten pregnant doing so, no less!), I want to tell you why.