It means you are doing very, very, very well right now. You're good mood is great. Your humour is great. Etc,....

you are on fire = you are on a hot streak = you are doing great = you are in the zone

I'd like to see Eliot on fire. :P

1- A term that people use when someone is doing great and they are unable to be stopped. Man, that dude is on fire 2- A state of mind in which people believe that they are unstoppable and can do anything they want--and they do. Allen Iverson was on fire, he was making every single shot he took. 3- a state of being when something or someone is engulfed with flames Guy #1: Hey man, that guy is on fire Guy #2: Holy crap! should we get a hose or something? Guy #1: Naw, just tell him to stop, drop, and roll http://www.urbandictionary.com/define.php?term=on+fire

"you are on fire! = you are alight and literally burning / you are very enthusiastic and full of ideas