Six men in Harry Potter, Daniel Radcliffe (Harry Potter), Rupert Grint (Ronald Weasley), Tom Felton (Draco Malfoy), James Phelps (Fred Weasley), Oliver Phelps (George Weasley), and Matthew Lewis (Neville Longbottom). The name "Sexy Sixy" was created by two girls at a sleepover so they could refer to the men easily.
Girl One: Who's your favorite, Daniel Radcliffe, Rupert Grint, Tom Felton, Jam--
Girl Two: Why don't we call them something else? Like... the Sexy Sixy?
Girl One: That's a great idea! So, who's your favorite Sexy Sixy?