Had a GOJET tool jump on my flight one day. I was late to the plane due to a late connection. I was told about him by the FO who said he checked his credentials. Since we were late, we push and start to taxi. As we taxi we get informed that our flow time is now 2 hours later. Ok, back to the gate and the toads off the plane. As we are reboarding I am standing at the gate and a pilot looking dude comes up in sweat pants and a t shirt. I ask him if he is our jumpseater. he says yes and introduces himself. I ask him if he often jumps in seats. he says he is allowed to on his plane. I made him change and told the gate agent if he didnt make it back in time that he didnt get to go. Turns out he was in his uni and changed while we were waiting out our delay. tool!