When a friend tells you to use a hoe on the knapweed (so your arms don't turn into itchy, red, burning, angry rash-y things) and you reply "what's a hoe?" (joking, of course). And she replies with this.
I use this cartoon in a presentation that I've done on gardening where I emphasize learning to live with and utilize weeds. I tell folks to remember this cartoon when they're attempting to have "clean" gardens so they realize how ridiculous that notion really is.