In the Satanic Bible by Anton LaVey in 1969, what does this verse mean...?

Don't do good things for people who don't appreciate it. In other words, don't get used or manipulated.

Good question

A hero is one who vanquishes his enemies. Too many enemies and he will fail and become a martre instead. So a small sprinkling is about right - like spice.

People who do good only to be slapped in the face in return are loosers.

Of course all of that is from the insane ramblings of a low class carnival organ player who wanted lots of sex. He was a little man with a small organ. Not worth mentioning actually. He was very silly

Simply that it isn't worth doing good to people who don't appreciate it. Satanism to a large extent is about putting number one first and satisfying your own ego, and if you don't you just look like a weak idiot to other Satanists.

well the first sentance makes sense, what doesn't kill you makes you stronger and all that. but doing good and getting sneered at just makes you the better man/woman.

It means LaVey was an egotistical blathering nut.