Why do people use the phrase "you mad bro?"?

[Thomas]

I said honesty said this once on twitter and facebook, apparently. Someone told me to please never use this phrase ever again, at first I didn't understand why. How I see it as people saying that phrase, when someone is mad after a game. I looked google to find out what it means, besides of what I was thinking. Their were a few definitions to it, one was someone who's trolling or being racist is another? I couldn't believe I wrote that, I feel regretful and disappointed. I feel so stupid right now, but why do people feel the need to say this? This phrase is not a cool thing to use, I highly suggest people who read this to never ever use this phrase. I've learned my lesson tonight as of using that phrase, I deleted my status was recently updated and I officially deleted it. I don't about the likes I received anymore. I'm finally glad but disappointed at the same time that now I know not to ever use this phrase. Why do people come up with these phrases?

[eddie]

I hate that phrase

[Devin]

Are you upset, my friend?

[SHEP]

It's a way of excluding half the population from your discourse.