Guillermo Montoya is widely regarded as the best tennis player in the world. In Everybody Was Best Friend Fighting he meets Hannah, Lola and Mike backstage at one of Hannah's concerts. His partner for the "United Peoples Relief Celebrity Pro-Am tennis tournament" sprained her thumb speed-texting. Hannah offers to fill in although she can not play tennis. Because of this and because Lola and Mike are fighting during the tennis match, Hannah and Guillermo lose it.
Guillermo Montoya is portrayed by Michael Steger.
-"One little itty-bitty thing, Guillermo Montoya never loses! Never!"
-"Never? Not even in a little charity game? You know, for fun?"
-"Fun is for losers!"