For the love of christ, if you're going to cut your floppy hat make sure you have a full length spare.
People you don't even know who would other wise never give you the time of day will go out of their way to jack you up for having that. People in Kaf go berserk over it. You're probably better off wearing a hat made out of beaver pelts and unicorn skin.
If you're still unconvinced and you end up doing it yourself;
Cut all the stitching around the edge of the brim. (There is a piece of material that goes around the hat that connects the top and bottom along the side if that makes sense)
Take the brim piece off. Cut off only one small increment around the brim. I used one layer of stitching for a guide.
Resew the outside piece back to the hat.
Look at yourself in the mirror and take hero pics.
Lots of guys I know cut down their hat but they over did it and when the put it on afterward it looked retarded. It doesn't seem like a lot when your cutting but when you wear it it looks like the british floppy hat, or worse.
If on your first attempt you didn't take enough off, repeat the process. Better the extra time and effort then either looking dumb or lying to clothing to get a new hat.
