1. First and foremost, ignore. Remember they are nothing without an audience or a victim. They relish at the thought of someone even having a reaction about what they just posted and that's their motivation to keep coming back for more.
2. If you can't ignore, block. Out of sight, out of mind. And despite how tempting it is to check those hidden posts, don't. You know that the troll isn't going to say anything constructive or useful, only something that will provoke other people to post more --so don't even bother.
3. Don't talk about the troll. It'll only invite the troll to come join in the conversation and you're giving it attention again.. which is what they want. Get it straight in your head, negative attention is the troll's cheap laugh especially if you're making it clear that you were affected by what the troll said.
4. Do NOT feed the troll. By responding to its posts, you are hereby, guilty of FEEDING them by giving them a reason to keep posting and posting more responses.
5. Just post around it. Respond to other people in the thread or thread topic in question like you usually do as if you've never seen the troll's posts. There is nothing more sorry a spectacle than a troll who has zero responses to its futile attempts of getting people to pay attention to him.
6. Treat it like it doesn't exist. Yelling, trying to reason or reprimanding is pointless. Talking to them will have no effect whatsoever, no matter what sources you pull, whatever quotes you may have made to make your point.. say it with me:
It. Will. Make. No. Difference.
7. If all else fails, report to proper authorities to have their account suspended... or banned. :)