to eat your hat means to disgracefully, and shamefully, and embarrassedly, or pissed.offedly REALIZE you are wrong about something, or that somebody else was able to do something
like writing, singing, painting, posing, pimping, etc better than you can. kinda like having to eat your own words, but without you even having to say something first.
"biggety small sack saw stinky dopey dawg's new vid
and his shorty, latanyaneesha told him "guess you gones to have ta eat your hat now, huh, bitch".
to which small replied "slap!"