Relevant

I KNEW you we're going to post that. That was actually was I was going for with my OP.

Volunteer work!

Martial arts... just make sure you find one you enjoy with a teacher who's competent. If you do start then purchase some form of punching bag to punch and kick to learn to get the strength behind and punch properly; you'll seldom learn that in a lesson as you spend most your time punching air and even contact is light in most. Point based sparring is great fun if you really want to get involved and do tournaments etc but again they tend to teach you a few bad habits such as avoiding the best areas to hit should you find yourself having to use your abilities in real life.

I don't know what you have in your area but karate is generally the most common. It teaches some powerful punches and kicks but it's a little rigid and the best stuff is learnt early on usually.
Kick boxing is popular with the ladies if that's what you're after but bare in mind there are exercise variants of kick boxing aimed at women which usually aren't up to scratch if you want some practicality.
Regular boxing (which is quite different from kick boxing) can be brilliant for stamina and resilience but it can be an unfriendly atmosphere compared to most.
Jujitsu is a pretty good all rounder and has some good focus on multiple combatants. It's one of the most complete martial arts taught as well as it covers a bit of everything.
Judo is a good complimentary one for learning balance and understanding your weight and your opponents weight, falling correctly etc and can also be a good spot for ladies.

Ultimately though if you can shop around try a few lessons of various ones and find what suits you and your body.

Well, find a local Go (boardgame) club. As a bonus, atleast in Finland most of them are located in quality bars :)

I made my friends playing AD&D around the mid-90s.

Now, about 9 months a year, I referee pen&paper role-playing games for a bunch of teenagers at a youth center every Monday night (yes, I get paid to do this, crazy right?).

They are aged 12 to 17 and I have 6 hardcore regulars and if you count the semi-regulars, it adds up to about 10.

Computer RPGs have displaced pen&paper for many, but for the most imaginative types, the constraints of a computer program with pre-scripted scenarios doesn't completely fulfill their craving for a completely interactive world where you can do truly anything and get feedback, not to mention having an actual non-deterministic impact on the story (most computer RPGs have 1 way events unfold and if you're lucky, maybe a handful of branches) and also enjoying human interaction along the way.

I think the main obstacle for this for most groups is having access to a skilled referee. It does take some skills to realize the full potential of pen&paper.

However, I think that until they invent AI programs that can be truly adaptive like a human, there will always be a demand for pen&paper.

Join the army.

Actually that.

Another vote for pen-and-paper role-playing games, and board games. My brother took me to a board game night about three years ago, where I played Arkham Horror with a bunch of people I had never seen before. It was quite confusing, but I persistently attended such events because I found the game interesting, and what do you know, I eventually got acquainted with the people as well. I now consider most of these people some of my best friends, so that one night paid off pretty well.

Just a reminder, I met these people and, crucially, stuck with them because we share a trait: we're all nerds of some degree and thus found each other's company easy to tolerate and even preferable to that of most other people. If you have to force yourself to do something in order to meet people, you're probably doing it wrong. Nothing wrong with trying out something new, though; if you enjoy it, good for you. If you don't, I would recommend against continuing.

EDIT: Also, don't join the army. I can't speak for everyone, of course, but during the six months I had to serve in the Finnish military, I made one or two friends. The rest of our battery (some 150 people or so), not to mention other units, I considered with studied indifference or mild contempt, so the friends-to-nonfriends ratio was pretty poor.

astronomy? paint balling? yeas i know there different but it depends on your sociability type

r.e. the national service / vs armed forces thing. national service will likely have a different friend ratio than normal.
I still have friends from recruit selection and that was only a 3 day event (in this case). im not suggesting this is the way to go for that reason but just a thought i had when reading the above comment.

In my day parents would have been very frightened to know their kids were playing the devil's game "D&D". Thankfully my parents had no problem's with it. It's good to know the religious nuts are no longer so vocally opposed to D&D. Then again you are way up in Canada, very far away from the Bible Belt.
Yeah, the Army and Marines tend to be your jock type (there are always exceptions). The Air Force, Coast Guard, and Navy are more for our kind. I would advise most people to go to college before even thinking about joining. If you still want to join after graduation, at least you have a degree in your hand to become an officer.

Pen & Paper RPGs, of course. Absolutely ideal for what you're after. There are lots of places on the net where people are looking for other players, so it should be easy to get a group going. Unless you're living in the middle of nowhere, in which case you're fucked anyway.

Sports are great, too. Or book discussion clubs, writing workshops and similar creative or artistic endeavours, if that's your thing. Again, the internet makes it easy to find out what's going on in your area.

There are good things about volunteer work but I don't see any fun in it. :)

depends on what yer doing - it's not just about old peopels homes or charities.