I think having a 'speak to them as I'd like to be spoken to' rule is what I aim for. Obviously, within reason; "get down off the windowsill immediately", might not be how I wish to be spoken to, but it's necessary sometimes.
Looking at the wider picture and some of the other comments; I think there are different ways of speaking within families and groups of friends. It isn't really fair to make assumptions about those imo as some things sound a lot worse in writing or if they're overheard in passing.
For example, I wouldn't like to swear at or about a child, I have definitely thought my DH is being a 'bit of a dick' occasionally. He's thought the same about me and we're usually pretty straight with each other, albeit in a very lighthearted, jokey way. If we were genuinely angry with each other we'd probably be a lot less jokey.
I've thought the same about most of my friends and family at various points. I've heard a million times between friends and family, "stop being a dick". It's a joke and not meant to be as damning a thing to say as it might sound to outsiders.
So, I think to say you can't even think "he's being a bit of a twat today", or say that about someone, "even as a joke, because it will create an internal dialogue and colour how you view them" is a bit much to me. I love my DH and friends and don't think the fact that we have a bit of sweary, (not very witty, admittedly), banter between ourselves creates an internal dialogue and colours how we view each other.
How many times have I heard, "he's being a little pickle / little monkey / little rascal today" said about children? I sometimes think that's polite talk for "being a bit of a pain". It's just the choice of words. I won't say what I say about my DD if she's having a bad day and we're driving each other a bit bonkers; not because it's terrible - it's not, but because it's very outing!