Uh oh! Looks like someone has a case of the Mondays!
Many moons ago, while heavily doped on painkillers, Tet apparently sat bolt upright out of a doze, loudly exclaimed "I LIKE CAKE!" and promptly passed back out. So, we verbed it! "Liking cake" means to either be totally out of it, whether by fatigue, moping, a hangover, or medication. Hence why Vinci & Arty sometimes blurt out "I like cake!" in the strip.
This one was fun! Vinci has on his SULKFACE.