The comedy here comes from the use of the 'pun' form. The TV show 'Chappelle's Show' featured a number of sketches recounting the antics of now-deceased musician and bon-vivant Rick James. The sketches would typically culminate in the phrase 'I'm Rick James, bitch!' Now we look to the name of the shop 'I'm Rick James Bricks'. Clearly this is a reference to the aforementioned catchphrase. Although we cannot be sure from the photo whether the owner is called Rick James, we can say that enough comedic resonance is achieved by the similarity of 'I'm Rick James Bricks' to 'I'm Rick James, bitch!' juxtaposed with the fact that Lego indeed consists mainly of toy (emphasis) Bricks.