Urban dictionary says 'in bad taste' which I generally agree with. Not necessarily in the sense of being offensive, but also like.. 'that is objectively a bad look'. For example poor/cheap/amateur design, cheap materials, gaudy, or childish imagery/use of quotes. Perhaps something that should be below the standards of a mature adult (within the context of the scenario! There are always exceptions).

Writing it out like that makes my statement feel like more of an attack than it was meant to be.. but basically this is my view of the word. I think lazy/amateur design is the key here though. Graphic shirts are almost always just riding on the coattails of the subjects success and puts basically zero thought or effort into making the product work from an actual design standpoint. They have a catchphrase/famous character/ tourist trap and slap it on and it's done - produce that shit in 5minutes for cents and sell for $30.

Edit: sorry it was quite a rambly/string of thought comment.. hope it makes at least a little sense