... when you start using "for the win!" and "fail!" in regular speech.
... when you've ever solved any argument during a friendly gathering (eg. house party, dinner at friends, whatever) by saying 'Let's Google it!" ... and they hook the TV and the computer together so everyone can see who gets Pwned when their side is wrong.
...if you had to Google 'house party' so you can understand the above.
...if you are replying to this thread because your usual MMO is having server downtime and you need some kind of fix to keep you going.