Top definition
A black magic spell used by people from Britain and by rich snobby bastards. The spell works by using it in a sentence to tell people not to do something. This spell is very dangerous. Every time it is used, all the planets in our solar system move 5 miles closer to the sun.
Guy who speaks normally: I'm gonna go fuck my sister.
Guy from London who uses said black magic spell: You must'nt commit incest. It is illegal.
Guy who speaks normally fucking died and the sun devours Mercury.
via giphy
Get the mug
Get a Must'nt mug for your bunkmate Georges.