During the act of sexual intercourse the man will go ball deep and insert his two testicles up the womans anus. It is said to bring a strange pleasure, especially when the testicles are removed and the famous "clack, clack" sound is heard.
1)"Oh mate was full maggin a girl last night and my bollocks have never been more supple"
2)Ollie: "Hey i shagged that girl last night"
George: "Wow did you full mag her"