My parents' most annoying habit is that they both mumble to each other and they never seem to hear what each other says, so are constantly saying 'what?' & repeating themselves loudly and with a deep sigh.
My DH and I are just the same now! 'huh?', 'eh?', 'what?' - followed by OFGS 'I said...', 'don't shout', ad infinitum.
Anyone else have parental habits they hate?