Is calling people by their first name considered disrespectful in Islam?
For example, I am part of 2 cultures. 1 culture considered it respectful to call people by their first name no matter who they are and what their age is. For example, in 1 of these cultures, it is perfectly respectable to call your granddad by his first name.
However, another culture I am part of would consider that disrespectful. This second culture says that a granddad should be referred to as granddad only, and should never be called by any of his names.
So in the first culture, if your granddad's name is John Smith, it is perfectly respectable to call him John, and would be considered weird to call him granddad.
And in the second culture, if would be considered disrespectful to call your granddad John, and would be considered respectful to call him granddad.
Does Islam have rules for this, is it considered disrespectful to refer to your granddad as granddad, or is it disrespectful to refer to your granddad via his real name?
Sunni view preferred with evidence from quran/hadith and/or fatwa.