Asking me if you can "jam on my guitar" is like asking me if you can sleep with my girl. If anything, your chances of me okaying you sleeping with my girl are exponentially greater.
true story: girl crying, calls me up and says her fiance left her a note out of the blue saying, "Babe dont worry about me, I'll be gone for 2 days!" I'm thinking she needs a drink or two with me tonight!