You like the endings. You hate the endings. You only like ME1. You only like ME2. You only like ME3. You love Bioware. You hate Bioware. You don't play multiplayer and resent its mere existence. You solo multiplayer platinum for funsies. You like Liara and wish you got more time with Liara. You hate her because she takes sceentime away from your favorite character. You tolerate ME1 combat. You love the Mako. You hate the Mako. You believe IT. You want to burn IT to the ground. You hate romances. You only really play for your space waifu/husbot. You only play femShep. You only play Broshep. You have played every permutation -- class, renegade, paragon, the whole nine yards. You only play on insanity. You only play on casual. You hate mods. You love mods.
...I could go on. That's just ones I've seen brought up as grounds for being a true Mass Effect fan.