A term meant to be used with the movie "The Avengers", a costume boner refers to any point in the movie where Loki's long-horned helmet and cape suddenly appear. This usually happens when he is exerting some type of power, such as when he instructs an entire crowd of people to bow to him and they obey. Much like a penis might become erect when the average male gets excited, Loki's costume tends to appear in similar events.

Got the covid-19 vaccine