I use Wikipedia quite a lot, and only occasionally spot acts of vandalism. But here's one possible example, from the entry on Tolworth (check out the final sentence - and click on the image to see a larger version):
Yes, it says: "I have been here and its not all that to be honest just a bunch of old folks".
Wikipedia defines vandalism as "any addition, removal, or change of content made in a deliberate attempt to compromise the integrity of Wikipedia". However on the same page it also makes reference to "unintentional vandalism". Huh?
Anyway, I'm not sure whether the Tolworth edit is deliberate or unintentional vandalism - or whether, in its own way, it actually adds to the article.