to insert a tampon.

putting in your headphones to be left the fuck alone

When you haven't ejacated for so long that you're pent-up and cranky.

When a girl takes 3 dicks in her mouth, 2 in her pussy, and 1 in her anus simultaneously.

When a females blood cycle is occurring and she needs a tampon to keep it from bleeding.

How one would say the phrase, "plug it in" in the UK.

To engage in the sex act of double penetration(or DP for short), which is when two men simultaneously insert their penises into the woman's vagina and anus. This term can also refer to when three men bang the chick the same way, with the third man inserting his penis into her mouth(getting her to be airtight).

And for your information, there actually exists a porn movie that was named "Plug Her Up" and that movie is all about double penetration as well.