How to tell my dad??

I can see where your parents might be upset, but that's only because I grew up right on the cusp of internet and social networking being a huge thing. I think Facebook was just starting to become really popular when I was in highschool, and for quite a while I operated under the assumption that everyone online was a liar or scam artist or creepy pedo, but these days that's simply not true.

The phenomena of making friends, and even romantic connections online has kinda exploded in the last decade, and it's not uncommon to hear from people with completely normal social lives and dating lives talk about Facebook friends or online gaming friends. The way people interact is changing and there are loads of articles online about the psychology of internet relationships, how common they are, etc etc that you might want to read up on before talking to your parents.

Mostly, I'm sure that they are concerned for your safety. Do a lot of research on how to keep yourself safe online...how to avoid sharing personal information if need be, how to verify someone else's identity, and safety precautions if you decide to meet someone. Show your parents that you are educated about the possible dangers and that you are making intelligent, informed, cautious, adult decisions when it comes to interacting online. If you do this, they won't really have a leg to stand on as far as their disapproval goes.

Meeting someone online is not so different from meeting a stranger at a coffee shop, except for the fact that they can conceal certain information. Point being, that when you meet someone in real life, you have no way of knowing what kind of person they are either, if they're safe, etc. you just have to show your parents that you're being catious.

Also, if I were you, I would have a serious talk with both of them about the pressure they're putting on you, and the fact that it's increasing your anxiety and not helping your troubles with social interaction one bit. Badgering someone who's a bit shy about getting out of the house is pretty counterproductive, IMO.

Tell her about the time you accidentally overheard her and your dad having sex and how it scarred you.
That should be awkward enough for them to leave you be

If you're over 18 tell her to mind her own business. It's your life and you won't be happy if you worry about doing whatever your mom wants.

Move out of the house, get a job and take care of yourself. Then you don't have to listen to it. If you think your mother is a buzzkill then imagine just what a buzzkill it will be when they are not around anymore. You will sing a different then. My mother died when I was younger and I miss her everyday. I wish she were here to bust my chops about something again. But it sure gets lonly with nothing but cyber friends. You can't get hugs from your computer and a friend is pretty nice to have when you are cold at night or need a real shoulder to cry on. You need to have interaction with real people not just a bunch of words on a monitor. I think you should appologise to your mom for being such a spoiled twit and ask her to help you find a friend who you will like. You might just find a real friend is the best friend of them all.

My best friends are from other countries and they are online friends,

everyone is not pedos online.