Erm, no. I can't say that I have.
I can honestly say that I haven't even thought about doing it either.
In fact, as I write this, I'm struggling to recall a character whose death sent me into a flying rage which is the state I'd get ranty -respectful or otherwise - and I can't think of one.
I've been saddened by the death of many a favourite character before, a little angry sure, but never enraged.
I think you'd have to be truly incensed to send a howler to an author over what they chose to do with a character of their own creation.
My propensity for getting emotionally involved with fictional characters is a running joke amongst my family and friends but I obviously just don't care enough about their deaths.
However, you switch this around and make it about romantic interests doing shitty things or bad things happening to my favourite couples and I'd be tempted, lol.
That's one of the reasons I read romance... You're almost certainly guaranteed a happy ever after!