I've had this little guy for about 15 years now. I bought him as a wee, 2 inch tall pin cushion cactus in the Las Vegas, Nevada airport returning from a trip to the Consumer Electronics Show. He was sooo cute (and only $3). For a long time (years?) he never grew, but he never died either.
I re-potted him on a whim, only to discover that instead of dirt, he was potted in plaster, likely to prevent spilling in transit. I stuck him in a little dirt, sat him in a south-facing window and watered him virtually never. Unlike Mr. Ficus, who I see has decided to turn yellow again in protest over new fertilize, the cactus remains content with tap water and sunlight.
And so the cactus grew, and grew over 15 years, and eventually split into two sections (now a tiny, baby third section has appeared at the base).
Every year, come end of March, he flowers. This always amazes me. A cactus is so perennially static. It moves in slow motion all its life and then in the span of a few short weeks it goes crazy with flowers. And then back to just sitting, and soaking up the sun.