I was about 13 years old and decided it was time to meet some sea lions. I bought a block of frozen squid sold for fishing, put it in a mesh game bag, and start swimming along Monterey's breakwater that is home to a large sea lion colony. Visibility was less than 10'/3M and it was getting darker.
I suddenly notice a strange momentary current that pushed me sideways. Weird, but I kept swimming. It happened again pushing me to the other side. Must be from swells hitting the rocks. The third time I caught a glimpse of a large black hole sucking up what little light there was... except with teeth. The wisdom of this adventure was immediately reevaluated, the game bag was turned inside out, and I reversed course at full speed.
Fortunately, some playful sea lion pups found me in Carmel Bay a few dives later where visibility was 4-5x better and mom was busy out of sight. I think the puppy analogy is misleading. It is much easier to ignore a puppy than a curious sea lion pup. Diving with sea lions are easily my most memorable.