The best road to progress is freedom's road. - JFK
Florida
Essay on editing Wikipedia
This troll is ready for feeding; note the collection of utensils on his belt.
A method of harassment sometimes utilized by trolls is to attempt provocation via leaving an unsavory message on a user's talk page, or somewhere similar where the user is destined to see it. In this case, the best response would be to revert, block, ignore. However, some users choose to engage with the troll, giving them the recognition they desire, which escalates the situation. This is commonly referred to as "feeding the troll."
If you witness a situation like this, it might be tempting to hound on the troll. (Do not insult the vandal.) But "troll food" is for trolls, not Wikipedians. The troll might try to eat you, if you attempt to eat their meal. Practice WP:DENY - do not add fuel to the fire, don't worsen the situation for the user at hand. Give the user a gentle push towards AIV, or whichever option is best depending on the situation, or file a request on their behalf.