Persistent or tenacious to the point of being annoying; stubborn and insistent (often with a negative nuance).
彼は執拗に同じ質問を繰り返して、ついに相手を困らせた。
He kept repeating the same question persistently and eventually annoyed the other person.
断っても断っても執拗な勧誘が続いた。
Even after refusing repeatedly, the persistent solicitation continued.
執拗な粘り強さは時に長所にも短所にもなり得る。
Relentless persistence can sometimes be either a strength or a weakness.