Often showing exceptional interest in computer games, tabletop games, movies and sci-fi shows. These individuals truly do not want to grow up. They don't realise you can enjoy all of these things in a super geeky fashion while also having a job, a car and possibly a girl/boyfriend. They simply focus all their attention into their hobbies and lose sight of the world around them.
Not bad, or malicious people necessarily. Just due to the way they've been raised, or the way they've dealt with the world. These people are probably going to live at home till they're 50. They often don't manage to settle down with members of the opposite sex for several reasons, usually a combination of poor self-esteem, poor self-management and the fact that they blame everyone else for their less than stellar existence. Most women/men find this highly unattractive and hence the adult child generally stays single either forever or until they finally do something about their situation and change their life. Some adult children occasionally meet other adult children and hook up. The majority of the time, both individuals will be massively obese, both suffer from depression and both stay at home all day while on sickness benefits. (because they're too depressed/lazy/fat to work) Likelyhood of their residence smelling of shit and unwashed clothes is high.
For the rest that never change and wish things will change without them putting the effort in. They will remain the same - they are truly lost.
"I wish I could learn to drive but I just can't afford lessons or manage the responsibility of driving. Ooo, what's that? Collectors edition of World of Warcraft for £70? I MUST BUY IT!"