a young boy who seems to be more grown up and acts manley, but is not yet grown often a child, can be a pet

A term used to reference cannabis/marijuana/weed.

An adult male who, due to a psychological or physical issue (often lack of stature) which gives them a complex of inadequacy , feels compelled to "prove themselves" to both friends and others on any given occasion by advocating and indulging in stupid and often dangerous acts of male bravado. The participants are often aided in these acts by their beer muscle.

Smallest Person in the group often referred to as a Dwarf or midget....

When playing drinking games that players can define rules, the little man rule is usually stated:
Every time you have to drink (not casually) you must pretend there is a little man sitting on your drink which you must remove and replace after drinking. Failure to do so will result in further drinking as a penalty.

A mans treasure, penis, knob, wiener, shlong

Little man is someone who is usually smaller than the usual height for their age and acts tougher than others because they play a sport. When someone is taller than them they will usually get on thier tippy toes and will put their chest out to look taller.