I recently blocked my first one, but it was due to issues on another site, not on dA. He just happened to have a dA account.
Me and my boyfriend (who's also on the site - that's how we met) were kinda sorta friends with him. He seemed friendly and nice enough and seemed to really like to RP so when he asked to RP with me I said yeah sure. He added me and my boyfriend on Skype. It quickly became apparent that he's really not good at RPing, though. I would respond with paragraphs and then he would leave like 2 sentences in script format (he's 21 so IDK what his malfunction was or why he couldn't seem to post normally). I'd get really frustrated, though I didn't tell him, and it just generally seemed like a pain in the ass to RP.
He would continually bug me about it on Skype though and even ask my boyfriend to tell me to RP. It got annoying real fast, but I kinda felt bad for not responding, so I ignored it and would try to leave a post when I could.
Things really escalated though when I found out that a mutual friend of ours, who'd been recently promoted to mod a few months back, had been having problems with this guy too. He'd asked her to RP and she didn't really want to, especially given his script-format thing, but she felt bad for him and he seemed nice enough so she went ahead with it. When she told him that she wouldn't be RPing for a while, and that she didn't want to write because of things her (now ex-) girlfriend had said, he got overly nosy in a way that made her uncomfortable. He also said that not RPing took him to a dark place and made him consider suicide. He obviously did this so she would continue to RP with him, which is honestly a dick move whether you mean it or not. This shit continued on for a while, and then when she was promoted to mod he obviously got really jealous. He kept saying how she'd always hated him, had never been nice to him, didn't understand how people with depression feel (nevermind that she was depressed and has been going through lots of real life shit), and wanted to ban him. He also left her tons of passive-aggressive messages that pretty much amounted to "I could be a better mod then you, I'm nicer to people, I've helped people talk out their problems instead of being mean to them, I'm like the site therapist", etc., etc.
This eventually carried over to me and one day out of the blue he just started trash talking this friend of mine and saying she had been harassing his friends (when I asked who it was, I didn't get an answer, and she said she hadn't talked to any of his friends in months). Fed up with all the bullshit, and seeing how unstable he was in some of the messages he left me and my boyfriend, I blocked him on Skype. Then the whole shitstorm ensued. He kept trying to message my boyfriend to get me to talk to him and even tried to call me on my phone Skype. He left several whiny PMs to the three of us. Then he made up some stupid shit about how it really wasn't him and how he'd been hacked. For seven months. On his phone and computer. And the hacker mysteriously seemed to leave messages that sounded exactly like him, to the same people he'd been talking to.
Anyway, he's still on the site and still trying to lie about it. If it weren't for the fact that the victim of this and another one of my close friends are both moderators he probably would've been banned by now. Unfortunately, though, a lot of people on the site who don't know better are his friends, and some of them have even been trying to stand up for him (even though pretty much anyone who knows anything knows that it's complete BS). It's been a week and a half now and the entire staff - including my friends - are completely fed up with him. I don't think it will be long now before he gets a permaban.
But yeah, that's my one blocking story. I get along with people usually and have almost never had to actually block anyone on any site ever, but this guy crossed a lot of lines. He didn't actually try to contact me on dA, but I figured I'd be proactive. So yeah, he's on my list, and will probably stay there.