An affectionate form of address, usually said by a man to another man, indicating your level of comfort with that person is equal to that of an old, well broken-in boot (as opposed to a cramped, new shoe.)
Thanks for letting me borrow your car, and loaning me gas money.
1:
two men driving rather fast and having to swerve violently to avoid an on coming vehicle andy's mate shouted "Fuck my old boots that was close yer twat!"
2:
you have just got home after a great night out and sitting in the middle of your room floor is the bigest turd you have ever seen ,reeling with shock and horror the only words you are able to utter is "Fuck My Old Boots!"