It's hurtful to disparage a persons sexual prowess.
Mary is having a tryst with her lover.
Mary wants to tell her lover what she thinks.
Mary tells her sex partner that he is a great performer in the bedroom.
Mary tells her lover that he is lousy at making love.
Mary's lover gain self-confidence and becomes a great parter to Mary and all his future lovers.
Mary's lover develops a complex toward women and has trouble with all his future relationships.