Way back in grade through high school I would say:
the reason you are unpopular is that you aren't good at anything, and therefore can't give anyone what they want - NOT some kind of cosmic mystical "bad luck". The people who are considered "cool" and "uncool" aren't determined arbitrarily, but by strength and weakness, having what others want - being good at something or not. So the only way out, is to get strong/good at something. I don't like it, and I wish it didn't have to be like this, but there's no other way.
Pay attention to what others are doing, what works for them, and if I don't like their specific answers, just use the general ideas and put my own spin on it. Do my research to find out what options are out there besides the ones I see every day since most of those don't seem to be the answer for me, and do some soul-searching to find what's important to me and what I'm going for. But you have to play the game, love it or hate it, don't drop out and retreat from life just going through the motions, out of thinking it's too hard/you're not good enough/you can't do it, or out of refusal to "conform". That will only lead to more misery.
Also, there's nothing wrong with liking fandoms, but to be relatable, you have to be able to talk about something else. Even "geeky" people want to talk about other things too, and the things that seem to get the most interest from people, are the things we actually do ourselves, NOT just the things we like made by other people.
In college I would say:
Stick with the accounting major, to get a safe secure stable life, and to actually go on the offensive against my problems which take my own money to fix, instead of just passively accepting my problems as "me", which will never work. It doesn't HAVE to turn you into a boring person - just look for a company that values "work life balance".
Continue the exercise I was doing in high school, it's a lot harder to get back into shape than it is to stay in it.
If I haven't already, get good at something cool, so I have something to talk about and so I'm not bored with myself.
Drinking and weed - not the worst, not the best. "Just OK" and not a big deal either way. OK to do here and there, but remember, it is not a conversation piece.
Don't sweat all the nonissues like subcultures, dudebros, bad boys, tastes I don't share, etc. Forget the party scene and the traditionally "hot" sorority type girls. No one is muscling you out of anything and you're not missing out on anything you'd really like anyway.
Don't get into doom-and-gloom stuff about peak oil, capitalism, diseases, and things like that. Don't let your mind run away from you.
And last but not least, don't look for political answers to personal problems. It doesn't have any answers for me. I won't find anything there except more of the same, more of what doesn't work, just going deeper into the victim story.