A throwback to the time of the "taming" of the wild American west, in whose various saloons prostitutes were often referred to as "strange," taming strange refers to engaging in the sexual conquest ("taming") of an unfamiliar ("strange") woman.

The term would certainly not be used when referring to one's own girlfriend, with whom we can logically conclude the man would have some degree of familiarity.

To control a woman's pussy, as though you were trying to control or tame a wild horse.

A straight male attempting to seduce a lesbian.