Is being outside with a knife (for self-defense purposes) legal in the U.S?

[Lewinsky Stinks, Dr. Brennan Rocks]

I believe that switch blades are the only knives that are federally regulated.... at least as far as selling them.

I did not know that there are federal laws on switchblades. I thought that simply all states except Florida chose to outlaw them on their own. But that was many years ago and a lot could have changed.