Scratch and Sniff

Alright, listen up, buttercup. This joke is saying blondes ain't too bright. The joke implies that the bottom of the pool smells like a blonde. You know, like how they say dumb people smell like pennies? But, like, chlorine-y pennies 'cause it's a pool. Face it, you probably thought the joke was about actual scratch-and-sniff stickers, didn't you?