Why do people use the race card? Your opinions?

I can understand if someone really does get discriminated against that is understandable, but I have had 2 situation where I have gotten told I was racists - all because I look 'too' white according to some people. I, myself, am actually Mexican although I don't look like my dad - I look like my mom. Tonight I got called a cracker/whitey from my upstairs neighbor and was told I was racists all because I politely asked them not to be hammering so late(11:15/midnight). After I explained I wasn't racists and I was actually Mexican she backed off. Frankly, I don't care if she is black, white or purple as long as she respects others. Just curious in your opinions why people tend to go to the race card. My cousin on my dad's side pulls the I'm mexican card and deserve this, this, and this a lot. A good friend of mine who is african american/mexican/white always tells me she is entitled to more due to all the struggles of our ancestors. Just never understood why people do it? Unless it is Truly called for which I have seen on a few occasions.