Two years ago I thought I'd forever be limited to forging friendships over the web and I'm still surprised to see how wrong I was. It used to be that I limited myself to talking with other Autistics or with strangers I'd talked with on gaming websites. I never found anyone interesting or comfortable enough to talk to offline before I met this particular group of friends--but they're so lively and downright persuasive, it's impossible for me to refuse to meet up with them, and any text-based communication is just too diluted for me to really enjoy. I find it funny now that I catch myself worrying more and more that I'm misinterpreting them when the talking's just text, since that was never a concern for me before. Skype's voice-chatting abilities make online chat much easier for me.
In response to the OP, specifically: Oh gosh--I know what you mean about worrying about online and offline personalities.
When I started using Facebook, I limited myself to making comments only if they seemed clever since I knew I had a habit of rambling when given the opportunity. But since my friendships started to boom right after connecting on Facebook, I started wondering whether I could keep it up and whether I should. I kept filtering myself to keep "in character" as this dorky, optimistic joker to the point where I felt I should mark whatever "serious" posts I made with a note basically saying, "I know this is rather out of character for me". I guess it's because a lot of my past friendships ended because of my negativity, that I developed this obsession in the first place, but over the summer, I gradually recognized they weren't going to leave me at the drop of a hat. I started being more open to posting my real ideas, and I think I've grown closer to my friends as a result.
I guess what I'm trying to say (in my own roundabout, long-winded way), is not to worry too much about being funny. People generally understand that comedy is pretty hard work. That being said, I think you should just take things at your own pace--if you're not comfortable yet talking with these kids, it's probably best not to force a conversation. But if they start talking to you, I think it does more harm than good to go on avoiding it in the long run. Take it as an opportunity to brush up on small talk, I suppose. If you're still worried that they'd see you as "bland", just remember that comedy comes easier when you're comfortable, anyways.