Jack is one of the younger Boomers at Nellis. He is the apprentice of the aging mechanic Loyal and as such, spends a great deal of his time at the base's hangars helping his master. In his free time, Jack looks out into the wasteland with his binoculars in the hope of catching a glimpse of Janet, one of the Crimson Caravan Company's employees whom he has a crush on.
If you are at 'accepted' reputation level prior to speaking to him, he does not give you the "go to hell" line, and instead says "I just say strange things sometimes, sorry" and moves on with the conversation like it never happened.
If you give Jack scrap metal, it increases your fame with Nellis. If you give enough (seems to be 50 units total), you gain instant idolized status with Nellis Air Force Base. You can steal scrap metal from all around the Nellis AFB (obviously don't get caught) and Jack will accept the stolen scrap metal as if it weren't stolen; there is approximately 16-18 scrap metal pieces in the Hangars alone, making it a bit easier to reach idolized status.
If you talk to Jack before starting the quest for the bomber, he mentions something about a lady in the water (you soon find out what that means). If you ask him what he meant by that he will say "Go to hell outsider" not letting you speak to him, thus not being able to get the rebreather. If you follow this dialog, however, Volare! will be somewhat more challenging to complete.