Song meaning
Greg Graffin: "Get Off is about a runaway roller coaster that represents the human race."
Jay Bentley: "Which is why in the middle of that song we have that part where all the guitars go down, down, down, and I do that high pitched girly scream. (...) Get Off is about life as a ride. Greg just wants to get the fuck off the ride. Which isn't really a great sentiment either."[1]
General
The scream in Get Off at about 1:21 is Jay.[2][3]
References