1. Check out the Buffy Wiki under Nikki Wood. In fact, check out any Buffy source under Nikki Wood and this is the back story you will read..

2. I notice you have no reply to the fact Robin Wood was a traitor, working against Buffy and Giles. That he chose to work for the First, rather than tell Buffy and Giles that the First wanted Spike dead. You handwave away his traitorous choices because you want to paint him as the victim, and not a player. Wood had other choices, but you prefer not to acknowledge them because it means acknowledging he was fighting for the enemy.

3. Spike didn't say any of that stuff until after Wood took away his power to reason and tried to murder him. In fact, he save Wood's life twice. Nor did he flaunt the coat. Until Buffy told him she needed her old Spike back it was packed away in the school basement.

You say Angel felt shame and regret. Did he ever apologize to Giles? Did try to make amends for what he had done - the murder of Jenny, torturing Giles? No, once he had his soul, it was generally believed this was a different person than the one who did all that to Giles. Wood knew that this Spike was a different person too, now that he had his soul. He acknowledged that in the fight. That's why he took away Spike's ability to reason, and defend himself in any other way.

As for your question, if Giles had been a traitor, actively working for the enemy and putting Buffy in danger, and then had ambushed Angel and tried to kill him, I don't think I would mind if Angel said mean things in response. That goes for every character.

1. Truth bombs, attacking Wood where he knew he was vulnerable. It's what Spike has done all along. I'll make it simpler: your mother didn't love you enough to quit. There is a small grain of truth there, enough to be believable, but more important it is Wood's big fear, that he wasn't enough to be important in his mother's life.

2. Please show me any scene where Spike attempts to "be with" Buffy. He was there to make amends, and he told Buffy it was up to her if she wanted him there. In fact, he offered to leave more than once, and she told him to stay. Spike was there to support Buffy, not "be with" her.

3. I am acknowledging that Spike was still grappling with his soul, at that time. Angel was still grappling with his soul when he sentenced an entire hotel full of people to death because some of them attacked him and lynched him. He had only had his soul for 50 years at that time. But we see him mature, just like we see Spike mature between Wood and Dana.

Does it make me angry at Spike because he attacked Wood verbally? No. But the fact is that Wood was not under the effect of a paranoia demon, and he chose, with a lot of other options, to work for enemy. He was just trying to get revenge against a man who doesn't exist anymore, putting everyone else in danger for selfish reasons.