25yo male with no friends or gf - what should I do?

You describe yourself as "boring" and "awkward" - does this mean you dislike how you are? Or is this simply how you perceive yourself? Do you like yourself as you are?

I like myself as I am - I just think that "boring" and "awkward" is how other people see me. I occasionally find people that have things in common with me that I get along with, but the majority of people I know aren't interested in the stuff that I'm interested in.

I know how you feel, I'm always super awkward too going and meeting new people etc.
I guess what I always tell myself is that ultimately noone really cares how you act and they might even start to like you especially if you get more confident as you get to know people. I find I get more confidence from being round people while the internet in general and staying alone gets depressing.

If you find something you enjoy like the comicons you mentioned there will be a meetup group for it. I joined a couple of walking/travelling groups through meetup.com and I found my main issue even while doing what I liked was being too awkward.
But I really dont think people care enough, so just go and be you and see what happens, just keep finding new groups and trying. I know how easy it is to give up , i keep doing that, i keep thinking well maybe i am better alone, but ultimately we're not.

As for girls no clue mate, they always want the over confident guy who will treat them like **** and I have never understood it tbh.

All i can really say is goodluck life is here to be enjoyed so find anything you like and do just do it, dont let anyone stop you as honestly they are not judging you on awkwardness the way we feel they are!!

If you're happy with how you are then just keep up with things as you are. It sounds like you're doing the right things and just need to keep at it until you come across the right person.

When you meet people, if you stall for conversation topics ask them about themselves. Use what's already been discussed to formulate new questions. Try to find common ground. You're on the right path. Just stick with it.

She told me she liked kinda nerdy guys and asked me what my type was and I replied...but then the conversation just went dead.

Don't worry to much of the outcome and don't get needy and desperate.

Do you have an ambition? Are you pursuing a career?

Are you partaking in your hobbies and doing things that make happy. Go to the gym and stop focusing on girls.

I hope this helps:

1) Relax, imagine you're just observing or there as a traveller. For example, if you are on holiday, you go there to experience and observe the attraction, you're not going to get anxious doing that are you?

2) Smile, smiling in contagious.

3) Be confident, respect yourself, accept yourself, work out, wear good clothes, feel good, focus on your passions, know you are a good person who treats people well, think positively, be proud of yourself, do things that make you happy, remember your happy times, what makes you confident? What makes you proud? Do you have a skill you are good at? Do things like cooking, driving, learning that increases your confidence daily.

4) Dress well, have good grooming, hairstyle, have good posture.

5) Just say hi or hey to people in your vicinity, who cares if they don't say anything back?

6) Ask how they are, how's everything, what made them choose this course, their plans for the future, their plans for the rest of the day, weekend, how was their weekend, what they will get up to, what they got up to, ask them about their hobbies, talk about the weather or did you see that sports game? Just mingle with them,

compliment them, say "I like your jacket". If you know they went on a holiday or somewhere, ask them about it etc.

7) Be passionate about life.

8) Lighten up, have a laugh, laugh easily, be friendly, approachable, interested, relaxed.

9) Look outside!

I'm not too worried about what people think of me, I know what my family and most of my work colleagues think about me. The problem is that I'm an ambitious person and I have high standards of myself - I worked hard to get my masters degree, work my way into a good job and get a mortgage on a house all by myself and I know that to have never had a gf and to have no friends at my age is embarrassing.

As for girls, I matched with one girl on tinder, I paid her a compliment and she was telling me how much she hated over-confident guys who wear tan and have man buns and spend hours in the gym. She told me she liked kinda nerdy guys and asked me what my type was and I replied...but then the conversation just went dead.

From the last sentence, I think you just need to improve on your conversation skills.
You can do this by learning new openers and phrases you can use to revive a conversation that doesn't seem like it's going anywhere.
For example use ask open questions to get more information which you can use to further your conversation so in that conversation you could have asked her why she hates guys who have man buns as that's pretty random
And lastly if it feels like it's going to die, end it instead of leaving it on an awkward reply
It seems basic but that's all there is to it really

I was thinking of trying to restart the conversation by suggesting it might be better that we text or talk on WhatsApp, rather than tinder, then leaving my number. That way she can message me if she's still interested, and if I hear nothing else I'll know not to pursue any further. Do you think that is a bad idea?

Dude, you are doing better than me. Im 23 yrs old never had a gf, only have 2 friends local to me, the rest live too far from me, only get the occasional whatsapp message.
Currently doing the whole videogames, tv shows thing you were, with a bit of gym thrown in. Unlike you though, I just failed my university degree, no job, no home of my own etc