…you’re watching an episode of Hoarders and notice that they’re tossing a BLUE, rectangular cooler and think “damn, I could use that as a mash tun!”
:o
…you go to Home Depot to buy something for work, and walk out with ONLY stuff for your brewing…
…your hops are taking up half the available space of an upright freezer. :
… you have absolutely no doubt you’ve got a completely rational, neigh pragmatic argument to acquire a third chest freezer for the garage in less than a year.
You own an autoclave and have a refrigerator with nothing but slants in it.
you spend more time posting about homebrewing than actually brewing.
When you’re at a pool supply store shopping for a pool filter and inadvertently stumble upon nylon mesh bags that can be used for dry hopping. Jack pot!
You buy a house after serious consideration as to how the brewery will work in there. 8)
That’s the plan! 
And/or spending a lot of time playing with/dreaming about brewery design - in that new space with CADD…
…your girlfriend really does know the difference between an Irish Red and a Flanders Red
… you have a hood and half the fridge is taken up by petri dishes at your apartment…
you have to have your room mate take care of certain brewing oriented tasks for you while you’re away for work…
You brew beer.
…when you already have 3 freezers and your wife comes home from work and says, ‘one of the Drs at work has a freezer for sale.’
When a package arrives and no one knows what it’s for but they automatically put in your brewing area because “It’s for Dad, it’s probably for his brewery”.
Paul
You think you’re low on beer when you have less than a 6 month supply of homebrew ready to drink.
Mine go even one better. When a package arrives, they call me at work and ask if there’s anything in the box that needs to go in the fridge/freezer
!
I need to tell them they’ve been one up-ed. ;D