Definition

1. little man syndrome
"Napolean complex" is already a term. The "little man syndrome" is less literate; unneccessary.

2. Little man syndrome
Condition whereby undersized men compensate for their smallness by physically asserting their presence.

That Puerto Rican just freaked on me when I stepped on his puma—he’s got a bad case of little man syndrome.

Courtesy of http://www.urbandictionary.com/

I'm not sure I totally agree though, I don't think that men need to be short to have LMS. I have known short men who are perfectly ajdusted, I have also know very tall men who have a chip on their shoulder larger than most boulders.