Being difficult unnecessarily, especially implying violence or actually threatening violence. Such an attitude usually starts a conflict. Refusing to chill or back down. Overreacting to minor slights.
When a sexual partner compares you subsequent partners they have had and provides you this compliment, it means you are one of the best partners they have had and that others that have followed have not measured up.
Bob, since I have been with you intimately sexually, sex in the summer, you have been a hard act to follow. lover, sex, partner