Yes - pestering, nagging, no matter what you call it - it's disrespectful. Sure, ask about the doctor's appointment, the event, the car - whatever. But, asking and asking and asking is NOT likely to change the answer. In fact, sometimes, I'll childishly put things off EVEN more if I'm repeatedly asked about it. Or, well, my no means no and I'll eventually just shut down/be non-responsive. Ideally, you say no and move on and if it comes up again, you say you've already answered that - maybe reiterate your answer. You can always leave a conversation, a room, your house, etc.