A sexual act between male and female in which the penis is inserted into the vagina, or as Stewie Griffin would say:
"Inert your pen-is ('pen' as in for writing, fallowed by 'is') into her vag-in-a (like 'Badge' with a 'V' fallowed by the two words 'in' and 'a')"
Quagmire was playing a sex game with an asian woman in his country house, and he was dressed as a geisha, then he took of his robe and positioned himself over her, and saw the griffin family had walked into the room. He then said:
"Oh.....is this the weekend you guys were coming up?.......Well here I am, cream on my face, hair a mess, and in mid-coitus, I must look a sight!"