Rap is the language of a man's soul is the fifth episode of Gurren Lagann Parallel Works.
The story begins with Gimmy walking naked through the terrain until he comes across a goofy version of Simon bottomless and waving. Gimmy attacks Simon with kancho, a traditional juvenile prank in Japan involving sneaking up behind people and poking them in the anus. This causes Simon to fly out of his trademark jacket, which Gimmy takes and continues on. He subsequently applies the same attack to Kamina, ending up with Kamina's cape and sunglasses.
When he comes up behind Yoko, however, she is aware of what he's doing and gives him an intimidating look. Gimmy starts to walk away but then he distracts Yoko and snatches her bikini top.
Subsequently, Simon, Kamina, and Yoko pursue Gimmy in Gurren Lagann—until Gimmy uses his kancho to attack and destroy Gurren Lagann as well. The scene shifts to a nude Gimmy, revealing these events to be a dream.
This is one of the two times Yoko's nipples are visible.
This parallel work is likely inspired from the director's cut of Episode 6, "There are Some Things I Just Have to See!!" when Gimmy misunderstood what Simon meant by "find a hole," and Kamina urged him to do the same to him in an attempt to see the girls nude on the other side of the hot spring. A couple of scenes from that episode are seen in this parallel work as well.