Mac: Pertinacious
From Dictionary .com:
per⋅ti⋅na⋅cious
[pur-tn-ey-shuhs] 1. holding tenaciously to a purpose, course of action, or opinion; resolute. 2. stubborn or obstinate.
3. extremely or objectionably persistent: a pertinacious salesman from whom I could not escape.
I think...