Ding dong belm

Can anyone help me?

I've just been discovered a new verb: to belm. It means to put your tongue between your lower lip and teeth, and pretend to be stupid.

I imagine it is an extension of 'doh!' and perhaps used in the same way as 'dur', which means, as I understand it, to imitate a scoper, the modern euphemism for a disabled person, frequently overheard in playgrounds to describe people regardless of ability. Children are so cruel.

Apparently 'belming' is common among online communities, and I imagine that it has an emoticon or acronym to accompany it. But unless it was first used in Lower Saxony, I cannot discover any etymology for the word 'belm'. All I can think is that it is a corruption of bell, which stems from the appearance of the chin while containing a tongue.

Hmm, I seem to have gone all pretentious. Unlike this fun balderdash and piffle precursor.

Any takers?