It makes you look like this. 
It is both an overused meme that makes you sound like an eager schoolchild mimicking a cooler friend, and a means of declaring your indifference to the quality of the English language. It dilutes the true meaning of “epic”. By using it this way, you are helping it plunge further into the bland depths of synonymity with “good”.
You are using it as it is defined in the OED: “Of the kind described in epic poetry; grand and heroic; impressive in scope; grandeur, etc.”. If you’re not talking about the classics, true heroism, or something genuinely grand, it is not appropriate to use the word. We suppose you can also use it ironically to make fun of the kinds of people who think it’s clever, but even that is becoming tiresome.
Please, link others here. You may also peruse the other words and phrases nobody should say or ruin.
Disputes and suggestions may be directed to SuitCase (Email link).