"I only take Viagra when I'm with more than one woman"

This quote by Jack Nicholson is a humorous way of revealing his self-confidence in his sex-related expertise. He is indicating that he does not need the assistance of Viagra to execute sexually when he is with one lady, however that he may need it when he is with greater than one female. This can be interpreted as a joke concerning his age, as Viagra is often used by older guys to assist with erectile dysfunction. It can also be interpreted as a joke regarding his sexual cravings, as he is indicating that he requires the aid of Viagra to stay up to date with numerous partners. In either case, the quote is a funny method of revealing his confidence in his sex-related capabilities.