A teenager hanging out with his friends in Brooklyn apartment was shot in the head when one starting playing with a gun yesterday afternoon. The victim, Marquise Perez, described as being either 13- or 15-years-old, is in "extremely critical condition" at Kings County Hospital. Apparently, an adult was home - Perez's 41-year-old cousin Victoria Rodriguez who lives in the Howard Avenue apartment - but the group of teens were in the back room. One of......