Mind honey is a special honey used in Sollux's Apiculture Networks, which allows the bees (who speak in beenary) therein to act as processors in a computer. He also feeds it to his Lusus in order to increase its intelligence, causing it to be an idiot only most of the time instead of constantly. Its brain-bolstering abilities affect Sollux far less positively - being a high-level psionic already, the mind honey causes his brain to overload and then blast giant eye beams of pure psychic power. Sollux has consumed it at least two times in Hivebent. The first time was while under Vriska's mind control where in he ended up killing Aradia and her lusus, as well as leveling her hive. The second time was accidentally while sleeping, which resulted in the destruction of his roof and his own lusus. Later on, he uses similar eyebeams in a fight against Eridan, and then again in a second duel later still, both without visual eating of mind honey, so it appears that he is capable of generating them on purpose under normal circumstances. The mind honey seems to simply increase the effect and render it uncontrollable.
Mind honey may be a reference to Problem Sleuth, in which Jocose Honey is used in Comb Raves.