I think that ranking high on the leaderboard, as a community, is good publicity for Code Review. I'd like us to rank high, and all members to get a lot of hats, but without abusing the rules, staying legit. Some hats are easy to get, while some are harder, or even very hard. (If it was easy, then what's the point anyway?)
How can we get the most out of Winter Bash 2015, without crossing some sort of lines?
Here's a list of common hats that may invite inappropriate behavior, and my ideas to get them legitimately:
Timey Wimey: this hat is received by editing old posts. Stick to your principles as usual. Make your edits count. There's plenty of old crap [reference link needed] that can be improved, take the time to find them, and improve the site while getting this hat. You may even come up with clever SEDE query ideas, post them for review (from a mobile app, perhaps?), and get more hatz & repz.
Thalia & Melpomeme: These hats are received from reopening/undeleting and closing/deleting respectively. Stick to your principles as usual. If you want to get this hat, spend more time on the review queues, and just wait patiently. You have 3 weeks, no need to rush, is there?
Greeter: Like Timey Wimey, make your edits count.
Hairboat's Revenge: This is the one that you'll find clogging up chat transcripts a lot. This badge is earned by commenting on Jon Ericson's only CR post. You can try to come up with meaningful comments, it's a good mental exercise. But the truth is, Jon Ericson had it coming. Meaningless comments are well expected here, and since they are cleaned up, they don't leave a nasty legacy behind on our beautiful site, so who cares, go knock yourselves out.
Speedy Delivery: This badge is earned by answering a question less than half an hour after it was posted, and subsequently earning at least +3 and being accepted. Someone once said that any improvement on the OP's code that would result in a commit is a legit CR answer. Also, you can post your most important point quickly, and refine it later. Totally legit. With just a little extra attention, I believe this hat will likely get awarded to all regulars. You have 3 weeks, no need to rush, is there?
Living in the Future: This badge is earned by selfie-answering a pre-WB post of yours. Well, hopefully you're all so much wiser and more learned since the time you posted your old junk, and there's a good chance you can write a decent review yourself. Btw, pimping such answers in the 2nd monitor seems fair game to me. (Not likely to have a lot of these.)
Auld Lang Syne: Posting a starred message with twelve hours of UTC NYD that gets starred. Oh so on NYD we'll all be a bit too star-happy? On an average day pretty much every regular gets starred within a 24h period anyway. Go knock yourselves out. I don't see anything wrong with a star carpet on the entire NYD.
Sun Wukong: Here's the one to watch out for: A hidden hat earned by a meta post with -5/+5. I don't know how to get this in a legit way. This hat sucks.
Vote Early/Vote Often: Earned by voting 250 times in 7 days. As the vote allowance for 7 days is 280, this is nearly equivalent to capping every day.
Stick to your principles as usual. If you want to get this hat, spend more time on the site to see enough stuff that you feel like voting up or down.
This is my favorite hat by the way. We always encouraged voting here, and more good(!) votes are a very good thing. I wish everybody went for this hat.
I'm Batman: This hat is earned by editing a question that gets reopened after doing so. Stick to your principles as usual. If you want to get this hat, spend more time on the review queues, and just wait patiently. You have 3 weeks, no need to rush, is there?
(If you already have it, and you see an opportunity, it would be a nice gesture to drop a word in the 2nd monitor to let somebody else do it and get the hat.)
I took the list of hat descriptions from @Quill's post, it helped a lot in writing this, thanks!