Coolidge effect

Etymology
First used in a 1955 publication by behavioral endocrinologist Frank A. Beach, to whom it was suggested by a student, in reference to a joke about US president and sexual promiscuity.

Noun

 * 1)  A phenomenon in animal species whereby males (and to a lesser extent females) exhibit renewed sexual interest if introduced to new receptive sexual partners, even after cessation of sex with prior but still available sexual partners.