Grond

[Mark Zuckerberg]

The long giant battering ram from Lord of the Rings: [The Return of the King] shaped like a giant flaming [wolfs] head

When you get a boner while grinding with a girl at a club, and it presses up against her ass. This term is used because a boner is shaped similar to [Grond] from Lord of the Rings (long and hard) and also because the word [grond] is similar to grind