So, I don’t know how accurate this website is, because it is a giant ad for DNA testing materials. However, it’s fun, so I’m posting it anyway.
This is a chart of all the possible ways to get DNA from someone who doesn’t want to cooperate. I’ll give you a hint. Hero walks into the bad guys office and gets a chance to snag cigarette butts or an envelope he just licked, smoking works for the hero’s advantage here. :D
On that same note, the heroine doesn’t need to try to get semen from the bad guy if the bad guy happens to have a cold.