Why do so many people misuse the word "myself" as in "Jeff and myself walked to the store." Even people I know are well educated say it.?

I don't like it myself, but so many people seem to do it that it becomes (almost) acceptable.

If you omit 'Jeff and' from the construction you give, anyone can see how absurd it is.

Was the person who wrote "I don't like it myself" trying to be funny?

Because it seems to be commonly accepted usage, even though it is incorrect. It is particularly grating when news reporters or people in the public eye a lot do it.

Because they don't know proper grammar like myself does.