Looking back on a situation or event, regretting that you didn't do what you should have done, and developing malicious ill will because of it. Similar to standard regret, but someone else is gonna have to pay for it.
One of the greatest composers of the 20th century. He has played on every instrument he wrote for. His works include Symphonic Metamorphosis and many other orchestral pieces. His most famous piece of work was the Symphony in Bb. It consists of 3 movements and is regarded by many as the greatest piece of band literature ever devised. Many people who listen to Symphony in Bb will think it is some sort of "circus of doom". Only musicians really truly appreciate the work Hindemith has done.
The Paul Hindemith Symphony in Bb is the hardest piece of music ever!!! Playing it right is the greatest thing you can ever do as a musician.
Someone who claims that the signs of the impending financial disaster were obvious all along, despite never having mentioned anything at the time or having acted to avoid it happening. More generally, someone who uses hindsight to make observations.
That guy has lost billions by trading in poisonous debts, but now he has a new career in the media as a hindscientist.
When your car's rearview camera gets covered in dirt from the road, place your finger over the lensin the back of the car, and give it a little hindswipe; you'll be seeing clearly right away.