Just remove optionsof.txt (I believe that's the correct name?), restart Minecraft and you'll be fine.

I have been having the exact same problem

The H command works (fn+F3+H), it allows me to see all of the useful information about an item and stuff

All you have to do for that one, that I have seen, is hold down fn and H at the same time, and then while they are down, push the F3 button, and it works like magic.

Yet for some unknown reason, the fn+F3+B command won't work, not even with the same methods I know the B Button isn't Broken for oBvious reasons...

Perhaps this page will assist in your search: http://minecraft.gamepedia.com/Debug_sc ... Debug-Keys

Any ideas, please help me

NOTE: I run 1.11.2

I'm pretty sure optifine isn't the problem.
The only other thing I can guess the problem would be is if one of the keys you need to show hitboxes is broken. Check them all (Fn, F3 and B) and then try it, if this doesn't work, try reinstalling 1.8 (delete the version in the versions folder of .minecraft)

IntellectuaryI'm using 1.8.0. I have OptiFine. I need to use the Fn key to use F3 commands. Please pleas help!!!

they actually will *facepalm* you just need to spam it because you pretty much need to press it the EXACT same time

This is seriously getting retarded.

don't delete minecraft . it will blow up ur pc (not) or Dinnerbone will look at u liek dis.

Don't never delete .minecraft!

I did try that many times. Do you think I should delete .minecraft and try again?

Im assuming you have a laptop by the use of the function key. I feel your pain to have that extra key in there.

Fn+F3+B all at the same time and it will show white hitboxes around any entity