An unsolicited critique of someone's work is basically an unasked for and probably unwanted opinion. Sometimes the people that give them out feel like they're doing the recipient a favour or giving what they deem to be constructive criticism. But sometimes, they're just being a dick.
Having somebody slate your work is one thing, but to do so maliciously just breeds contempt and jealousy in our photographic community. It's not needed! We each have our own artist vision, a way we capture images and we should have the freedom to freely post our art without fear of someone just being a dick.
There are countless stories of photographers who have been approached by one of these said dicks, who have proceeded to give an unsolicited critique and it has destroyed their confidence.
One story I vaguely remember is of a very good photographer who made a beautiful photo series, with all the photos having the same artistic feel (which most photo series have) and this dick told her that she obviously had this certain technique look nailed down, so she should try something else. He then suggested she buys a light tent from eBay... Because it would make her a better photographer! I'm sorry, but a £20 light tent for product photography will not make you a better portrait photographer. Period.
I'm sure he suggested a few more 'improvement ideas' after that, but the point is she gave up photography. One dick and his dickish opinion made her give up. She started again, but obviously it destroyed her confidence. The worst part about it is she looked at his work... And it was terrible! Like crazy terrible!
Unless someone has asked for an opinion on their work, how about we keep the critiques to ourselves. Let's keep the love in our photographic comunity.
Don't be a dick.