So, since Discord hasn’t yet appeared in Equestria Girls, I ended up making a design for him. Despite my better judgement he came out kinda hot. Some design choice decisions/headcanons below:  
So, while the original Discord might be a 2000 year old sort-of-god of Chaos, the Human World Discord is, well, a human. Just like Principal Celestia and Vice Principal Luna. Also, Immortals will change form with their power levels and mental state, but Human Discord is just a guy in his twenties. He’s also in a bit better or a mental state nowadays, but that doesn’t matter.  
Another difference between the two of them is healing abilities. Original!Discord is, as I mentioned, an Immortal and can heal from pretty much anything. So when Human Discord hurt his arm as a teen, it stayed.So his left arm is in a wrist brace all the time.  
Speaking of his outfit, you can bet it’s custom made.Everyone questions why he’s so Extra™.  
So, in EQG World, Discord is CHS’ Theatre teacher. He fits in well with the theatre kids. The shirt he’s wearing is from last year’s Midsummer Night’s Dream production. I actually own this shirt.  
Side note: he’s slightly taller than Celestia. And points it out all the time.