Sexual Intercourse.

[rubah]

(SPOILER)
Paper Clip -> Friction -> Lubricant -> Personal Lubricant -> Sexual Intercourse

[Timekeeper]

(SPOILER)Paperclip -> France -> Prostitution -> Sexual Intercourse

Haha I was going to go via the lubricant path as well xD

[Jiro]

(SPOILER)Paper Clip -> Lock Picking -> Burglary -> Sexual Assault -> Sexual Intercourse

You early people took the path I would've taken xD

[Quindiana Jones]

ROUND FOUR IS OVER. Original post updated.

[Agent Proto]

(SPOILER)Foundry -> Molding -> Plastic -> Latex -> Condoms -> Sexual Intercourse

[Jowy]

(SPOILER)Foundry > Magnesium > Plant > Latex > Condom > Sexual Intercourse

[Rantz]

(SPOILER)Factory -> Adolescence -> Adolescent sexuality -> Sexual intercourse

[G13]

(SPOILER)Foundry>Molds>Plastic>Latex>Condom>Sexual Intercourse

5

I'm sure someone else has this, it's like the only way I could find.

[Raven Nox]

(SPOILER)Foundry > Zinc > Reproductive/Sex Organ > Sexual Intercourse

[Jiro]

(SPOILER)Foundry -> Factory -> Hierarchies -> Feminists -> Pornography -> Sexual Intercourse

[Timekeeper]

(SPOILER)Foundry -> Zinc -> Reproductive Organ -> Sexual Intercourse

Dammit Raven Nox! Beat me to it xD
This one was the hardest yet, as far as I can tell there's no other way to get three, I'll keep looking though...

[Quindiana Jones]

I have no problem with matching results. Obviously, I can't check to see if you are cheating, but if you say you aren't I will trust your word. In a game like this, where everyone is trying to find the shortest route, it's highly likely that some answers will match. Don't worry about it.

Obviously, though, if you (one) do (does) cheat you're (one is) a massive goat buggerer. xD

[Jiro]

Confound it all! I should've taken the shorter routes instead of checking for matches. xD

[rubah]

(SPOILER)
Foundry -> Metal -> Cleavage -> Cleavage (breasts) -> Sexual Attraction -> Sexual Intercourse

[Peegee]

(SPOILER)Foundry -> Zinc -> Sex Organ -> Penis -> Sexual Intercourse