2.) A euphemism for having sex in general.
Originates from a line from the Bloodhound Gang song, The Bad Touch: "and we'll do it doggie-style so we can both watch X-Files."
Some Guy: But X-files has been off the air for...oh. Yes. Let's watch X-Files.
Some Dude: There's nothing on TV. Let's watch X-Files.
Some other Dude: Agreed.