The only way to explain the meaning of the word Mebert, is in the Mebert language, which consists only of the word Mebert, said in various pitches, volumes, and inflections.
When you're going down on your girlfriend put your lips inside her pussy and blow as hard as you can until you hear the sounds of a Mobertucky Muffler.
I left the Wabash with that girl from South Park and gave her a Mobertucky Muffler behind a dumpster.
An ancient beast of Norse legend. Half man, Half beast. It is large, in charge, and quite hairy. Most people, when first exposed to this beast, need photographic proof due to its alarming appearance. Characteristics include long hair, epic beard forged by Thor himself, metal tee shirts or rugby tee shirts, and a quizzical expression dawned before he feeds.
My sister was walking home alone last night and saw a large hairy beast leap from one building to another. She claims it was a Melbert."
The spawn of Carl Wheezer from Jimmy Neutron having sexual relations with Darla from Finding Nemo.
OR
An exclamation made while constipated on the toilet.