Why do men stare at other men?

My 16 year old cousin told me that when he's at the mall or somewhere a grown man or another male will stare at him. I didn't believe him at first but when we went to this mall out of town I watched as my cousin did nothing but walk to each department store and evry time we went to one at least one man was checking him out orgiving him a blank look. Now theres nothing wrong with how he walks AND he's not a bad looking young man that people have to stare in fact he's quite handsome. All I'm asking is why do men stare at other men like they satred at my younger cousin today? It's kinda scary