The saying tough as a pine knot means, well it means you’re tough! It’s a saying I’ve heard all my life and I still hear it often in my area of Appalachia.
The saying contains a vote of confidence from the speaker. I mean who wouldn’t want to be tough as a pine knot? Even if the phrase is said about someone the speaker may not care for, it is said with a grudging respect of recognition that the individual does have at least one redeeming quality-being tough as a pine knot. When I was young if someone said I was tough as a pine knot I could feel my spine straighten a little and my resolve to be even tougher solidify.