pertinacious

If you won’t take no for an answer, you’re pertinacious. The same holds true if you stubbornly push on a door despite a sign that says “pull.” Pertinacious means unyielding or perversely persistent.

We get pertinacious from the Latin pertinax, which combines per-, "thoroughly," with tenax, "tenacious." You can impress your friends by dropping pertinacious into conversation when referring to anyone who is bullheaded and obstinately stuck in their ways and opinions. If a Girl Scout is a pertinacious salesperson you might buy fifty boxes of Thin Mints when you only wanted one.