you're happy when your friends drink all your beer!
Possibly the best one on here. Bravo! Also probably going to be the best one that will ever be thought of, in all honesty, as it sounds perfect and absolutely nails all the things that make a great entry. But it doesn't really hurt that the incredibly vast majority of them aren't exactly playing the game entirely correctly either, strictly speaking.
(For example's sake, in case anybody wonders what the heck I'm talking about: "You look at your mashtun and..." - There! It's right there, in the very first words. If you personally have a mash tun to even look at, then yeah, you are probably a homebrewer, nothing further needed. The cleverness comes from coming up with a statement that best fits "You know you're a homebrewer when...," without making any explicit references TO home brewing. Sutepan's comment wouldn't sound like it has anything to do with homebrewing to a non-brewer (or even to many actual brewers, if said somewhere without an obvious homebrewing context), even if they somehow knew all the words and phrases of our vocabulary. Ultimately it's all in good fun though, and this isn't meant to be complaining; I'm merely expressing appreciation of one that I felt really hits the mark. But when it all comes down to it, just do whatever's fun for you!)