This list took some time to compile. I say compile and not complete because every racer probably has a few more bullet-points to add, so feel free to chime in! Don't assume that I'm saying I can do all of this stuff, because I can't except on very rare occasions--but I know plenty of fellow racers who certainly can!
You know you love racing when sometimes you flip your hog and you press "E" so fast that your hog never rests on the ground...
You know you love racing when you can enter the passenger's seat of a moving hog without it even slowing to pick you up...
You know you love racing when you know the map cycle better than the order of months in the year...
You know you love racing when you try to navigate Death Island with your eyes closed...
You know you love racing when you feel a maniacal rush of adrenaline upon spotting and driving straight towards that enemy hog helplessly making its way up/down the "stairs" on Gephy...
You know you love racing when you can type "hi," "lol," "ns," or even " red sniper" in mid hog jump...
You know you love racing when you can cooly face down, dodge, and nade that poor newcomer trying to chase you down...
You know you love racing when you can barrel over hills and bridges in a CTF or Slayer match, outshooting or outdriving all the unfortunate non-racers in the server...
You know you love racing when you can single-handedly defend your base in said server, sending Ghosts, hogs, and shees flying with bright blue explosions so long as you have plasmas left to throw...
You know you love racing when you know to head through the tunnel on Ice Fields after 1st nav, to avoid a slippery U-turn to head for 3rd nav...
You know you love racing when you listen intently after tossing a plasma from the passenger's seat, hoping to hear the soft tone of a hit...
And lastly in my compilation but far from least, you know you love racing, especially BFM racing, when you recognize the admins, take the rules to heart, and head for first nav with an itchy trigger finger, a sure hand on the wheel, and eyes peeled for an enemy rocket...
--boots