Steve and Toasters
Steve has, many times, run into problems with toasters. This seems to be the result of an unfeasible conspiracy against Steve; every time Steve attempts to make toast, something goes horribly wrong with the toaster. For example, various toasters have turned out to be fairies, Transformer-esque robots, or haunted.
Steve's problems with toast date even further back than these toaster troubles: at one point, Steve attempted to butter his toast only to discover that the butter had become a foul-tasting, three-eyed being.
Removal of Body Parts
Various appendages and body parts are removed frequently in this comic. In one case, an awkward situation arose when Steve discovered Moustache Guy's disembodied nipples while bathing in a hot tub (Comic 20). In another, Beaver somehow obtained another (or possibly the same) man's nose. Beaver once removed Steve's pelvis and used it to escape from the Shoe Goblin's clutches. And while playing a game of chase in Comic 144, Beaver accidently removes Steve's tail (which is an evolutionary throwback from the days when Steve's race had to escape the Sky-Octopus), which then turns into a minature version of Steve and tries to cut off Beavers' tail. (The real Steve then cuts off Beaver's tail and attaches it to himself.)
Steve's Inner Demons
Steve sometimes struggles with his inner demons, in a very literal sense. Steve's body has been occupied by actual demons who emerge every thousand years, a Lincoln-esque man in a top hat, and Loki, the Norse god of mischief.
Opening of Forbidden Doors
Steve seems to find it impossible not to open doors that are clearly never to be opened. In comic 159, Steve opens a door and releases the mighty and terrible QUAL'N'GURTHA, which leads to all sorts of unfeasible hi-jinks. Again, in comic 170, he smashes the 'Lovely Lock' that seals the portal between Pixie Land and Gremlinopolis, thus allowing the Gremlins to invade Pixie Land and enslave the Pixie population. Beaver in fact refers to this theme when he says "I thought we'd agreed: no more running gags."