I needed a good laugh tonight. Thanks for this one!
Not laughing at your woes.
It's just amusing, because though more extreme, I've encountered any number of parallels to this sort of behavior in my years as a gamer.
At least you can say your DM
is still a teenager. I've encountered men 40+ who are little more mature. There's still hope for this guy!
It can be tempting to run an npc with a party, to join in the fun yourself, but you need to have a lot of will power, a bundle of common sense, good taste and at least a smattering of diplomacy (the real thing, not the character skill) to do it well and not get abusive with it.
When I was about your age, we had an otherwise great DM, but one who couldn't resist including his own characters (just thinly guised as "npcs") in the adventures he ran. Invariably, the "npc" would save the day near the end, then berrate all the player charactes for how they screwed up and failed to do what he accomplished by himself. His girlfriend's characters(who were always madly in love with the "npc") would then swoon and get all gushy about how lucky we were to have met the "npc" in question. We tolerated that longer than we should have, but he -was- a really good DM, outside of that one particular flaw.
Unfortunately, I don't think we can say that about the guy running your game. Get yourself a higher quality DM.