I still can't believe I managed to cheeze this guy over first time I played... out near the Hydra where some likely open the door to him, I didn't open it... instead I just sat there and Zweihander R2'd him through the door... He dunk'd me three times in the process.
The RIGHT way to do it.
1. Defeat Mothra 2. Aquire Dwaynes key 3. Head to Dwaynes Basement 4. Use Dwaynes key 5. "Smell what The Rock is cookin'!" 6. Parry-Reposte+Backstabs all around.
On my first character, when I got to NG+, The first thing I did when I left Firelink was go straight to Havel, bare hand parry and 1-shot riposte him. I felt so satisfied because of all the shit he caused for me when I first started playing.