Rather than “so long and thanks for all the fish”, here’s the more direct approach “bye, and cheers!”. A kawaii cute dolphin raising a beer glass tankard with fish in it.
Available to buy at the following online stores:
You can find the design on t-shirts in most stores, but also on other products e.g. hoodies, mugs, clocks, duvet covers, shower curtains, bags, phone cases, notebooks etc.