The douchey guy that always brings his guitar and tries to act cool at parties or other gatherings. The conversation always comes back around to the type of music that he and his band are doing now or why his taste in music is so much cooler than yours. When the focus turns to someone or something else, he starts to strum loudly on his guitar or tries to get other musicians to have an impromptu jam session so that he can be the focus again. This guy is typically one of two personality types; way over the top happy or the brooding "too cool for school" guy. For an example, see Reverend Tim-Tom from the TV show on ABC named "The Middle."
Your friend Ethan is turning into "that dude with the guitar at a party."