One. I also wish there was a way to lay down ground rules.
Two I can post a few things on tumblr to remind people about how to act at cons, but I'm not sure if that would really help when it comes to things like people stealing from local businesses.
Three I think that massive internal teaching campaigns from within the fandom and people getting called out on their behavior in-person would probably help some, but this kind of thing is probably going to happen no matter how much people try to prevent it.
Four (I also don't think that other fandoms of comparable size and composition are really any better or worse, it's just that HS is more visible...and more body painted) This would be for the more general childish behavior, not the really major stuff like theft.
Five It's not like all Homestucks are like that.
I just highlighted some of the points I wanted to address.
One. ---- Well, maybe before each fanime, in the homestuck gathering thread, some rules of conduct by the one hosting the meet up should be posted. Something as a 'friendly' reminder. Maybe it's also time to talk to fanime about addressing this issue on their website itself and in the forums. The hosts of the gathering should also kindly remind everyone at the gathering too. Be like "Hey guys, as a fandom, we know Homestuck's got a really bad rep. So, this year, let's try and set a good example so that next year, when we come back, businesses won't be as wary of us." Or something like that. That would be a poor way to word it, but, you get the general idea.
Two. ---- I would post a general 'code of conduct' on tumblr for conventions in general, and when fanime 2015 comes closer, tag fanime 2015 and homestuck. Make it a point to reference fanime 2015 and homestuck in general.
Three. ---- Exactly. But, even if it still happens, at least it'd be a minority instead of a majority. Having massive internal campaigns would help a lot. I think maybe at the next fanime, if homestuck even wants to have a meet up at a business place, make sure you have the head of the gathering/meet up/whatever, pass around a collection jar for people to put money into and at the end of the meet up, present it to the business place as a 'thank you' for letting the group use the place as their meet up point and as a way for the business to somehow recoup some of their losses incase something gets stolen/the faygo sort of incident happens again. That way your bases are covered, and you can at least show that you're trying to be sincere and responsible for the group.
Four. ---- I dunno about that. I'm in a lot of other fandoms/seen a lot of other meetups, and I'm pretty sure that Homestuck is by far the worst. Not saying a fandom is better, but I've never heard any other fandom do what Homestuck has done. Yeah there may be some psychos or nut jobs in other fandoms, but in comparison to homestuck, it's like comparing an orange and an apple. Maybe it's because, like you said, the homestuck is basically running on the young crowd and the dregs/bad apples of the fandom that homestuck has such a bad rep, but I've never heard another fandom have the same kind of issues at fanime as Homestuck has had and I've snooped around extensively.
Five. ---- No, but enough homestucks are like that, that the fact that someone has to say "Not all homestucks are like that." as a defense just makes me feel like saying "Yeah, all homestucks ARE LIKE THAT." Idk, to me, that kind of a defense is like try to put out a camp fire with a pea shooter water gun...not very effective. I think instead, it probably would have been better to maybe say "I know Homestuck has a bad rep, and even though it's got a bad reputation, the older fans, the ones who have either just gotten into the fandom, or have been in the fandom a long time, have disassociated from really interacting with the fandom in an effort to curb their association with the overall negative image of the fandom." Or something like that. I think what Homestuck seriously needs to do as a fandom, all over the world, is revamp their image. I know in the past that Homestuck had a can drive or something. But maybe there could be a charity party called "Homestuck for the Holidays" around christmas time that collects donations for a children's charity or something, and maybe see if it can happen all across the U.S. or something of the sort as a way to offer a better image for homestuck, or at least detract from the negativity the fandom seems to incur.
Over all though, I just think that Homestuck will get a better reputation after the series ends and a couple years go by. Until then, if I were in the fandom, I'd probably disassociate from the fandom entirely and only stick around to read fanfiction/admire fan art, or talk with a fellow Homestuck enthusiast who you know is closer to your age, and overall, just avoid the Homestuck fandom's majority. But that's just me.
Wow, ended up writing more than I had intended, but this is just my take on everything.