In the simplest of definition, a man child is an immature guy who just refuses to grow up. This doesn't mean he necessarily lives at home with mom and dad ― although he probably should considering the way he functions in the real world ― but that he just doesn't have his life together.

When some little bitchboy is acting like a little tiny pee pee poo poo baby and messing up the group plans.

An adult male who still posesses psychological traits of a child. Traits include, but are not necessarily limited to:
- whining
- pettyness
- trying to pass the blame for their own underdeveloped judgement
- not "stepping up to the plate" when it's their role to.
- secretly still finds 3rd grade bathroom humor amusing.
- is able to connect with his children, but only as another child, not as a father.
- not to mention an overall insecurity in who he is as a man, from which similar traits sprout.

The manchild, if married, is often found married to Type A women (usually firstborn or only child in their own family) who reluctantly yet aptly take up the slack for the aforementioned manchild.

This manchild will often attempt to augment their lack and/or compete with peers with material posessions such as:
- Harley Davidson Softtail with $30 do-rag
- Hummer H2 or similar oversized fossil-fuel guzzling behemoth
- 6 seat felt poker table with matching humidor
- The very latest electronic gadgets (digital camera, GPS handheld, etc.) to impress peers with.

a grown man who is very immature, therefore considered a man child.

A male who is "of age" but still has the emotional/mental capacity of a child.

Completely incapable of making decisions regarding women, "manning up" when appropriate or discussing anything maturely, manchildren are becoming increasingly more frequent.

Manchildren will have notable traits such as thinking that they are somewhat different to other men because they have no emotional baggage, will find most immature humour widely entertaining and will have not been in a serious relationship, EVER. Longest relationship will be between 1-3 months.

When discussing important things, a man child will look at the floor and remain silent, pretend nothing is wrong at the time and then once out of sight drop into radio silence or will give you the "rabbit caught in the headlights" look.

However, man children are tempting challenge for women and more often than not an older women will take a man child under her wing as he will be impressed with her "at ease and coolness" and she will be taken back at his emotional naivety.

A man child is very easy to train in the ways of the bedroom.

A man child is a male who is over the age of 25, who still lives as though he is a juvenile. Many man-children are not gainfully employed, and survive off of the financial support of their enabling parents. Heavy video-game addiction to fantasy games such as World of Warcraft are key to the man-child.