The awesome feeling you get after attending a great gig (live show).
.Infallible belief that you rule
.Willingness to fight anyone who believes otherwise (if having just left a metal gig)
.Inability to stop smiling/dancing
.Feeling that all is right with the world
A gig high usually lasts for a couple of days before it fades away and you go back to feeling normal again.
Guy: "Damn, I am on a huge gig high from that Enter Shikari gig last night. I'm still raving several hours later! Man, am I awesome! Everything is awesome right now!"