Interestingly, the phrase "I'll eat my hat" refers to a "hatte" - a disgusting mixture of leftovers commonly eaten by servants in the Middle Ages if they absolutely had to (as a punishment, during war or if they were in dire need of food). The phrase doesn't refer to any item of clothing. It originated from the often ludicrous tales and rumours in servants' quarters. The message to be given out was "It's just as unlikely for that to be true as it is for me to choose to state that I will eat that muck". Slightly off-topic but it may be used in railway contexts: "If that's the onboard menu, I'll eat my hat" is normally swiftly followed by the eating of leftovers from the bin in the vestibule.