You can't make characters out of real people. I keep saying that in workshops. You know, you can take a little bit of him and a little bit of her and a pinch of, oh God, HIM?! and add it to the mix.
But try and squeeze someone you know into a fictional character - or more accurately, squeeze a fictional character into the straitjacket of a real person - and they just won't fit. The character has to have a mind of her own. Or she has to have reactions and instincts that don't belong to a real person, because she'll be facing situations that never happened in 'real life'. At least we hope they didn't, or you're going to get sued, OK?
(That's why Things Not To Say To A Writer no.34 is 'I'd better watch out, you'll be putting me in your book next!' No. Shan't.)
Revenge characters are subject to the same rules. I once read a manuscript for someone in which the protagonist's ex-husband was simply the vilest, most repugnant excuse for a human being I had ever encountered on the printed page (and so was his mother). And, you know, I've read quite a lot of serial killer fiction and stuff. I had to suggest, gently, that the writer should maybe make somebody up, rather than just (presumably) using her own ex. (Come to think of it, she never did speak to me again.)
I know this crime writer, though, who has a good strategy, not too in-your-face on the revenge front. If Mr McGinty and Mrs Craddock have offended him, the next (fictional) murder will take place at the Craddock McGinty Sewage Processing Corporation. In the immortal words of Pumbaa the Warthog, that's slimy yet satisfying.
That boy who once humiliated me in school, in front of the entire drama club? (Can you tell it rankled for a while?) I inflicted a terrible fate on him (in a book). He was even quite recognisable. But just to be on the safe side, I turned him into a girl first. After all (a) I didn't want to be sued and (b) for all I know, he's now a delightful, well-balanced, compassionate human being. People change. Snarl.
Fictional revenge. It's do-able. Of course one shouldn't. But one does. At least, this one does.
Oh go on, please tell me it's not just me.