Flattery is defined as insincere praise.
Until the 19th century, it was commonly thought that imitation was the sincerest form of flattery. Since this time, other methods of flattery have come into practice that are arguably more sincere.
The problem with finding the sincerest form of flattery is that flattery by definition is insincere. So something has to have just the right amount of sincerity to be sincere, but not be sincere enough to not be insincere, and therefore not be considered flattery.
Even though, or perhaps because of, or more likely not having anything to do with the fact that it is illegal and dangerous, animal sacrifice is one of the sincerest forms of flattery since 1087. Mimicry is a form of flattery:)
Rear-view-mirror decorationsJesus died for your sins, the least you could do is show him a little respect by hanging him on a cross from your rear view mirror. This form of flattery also works with McDonalds toys, stuffed pigs and yellow "Fan of [OBJECT OF ADORATION] On Board" signs.
With the invention of computers, copyright violation has become the successor to copying. With copying, you are saying to the creator, "yours is good, but I could do better". With copyright violation, you are saying "yours is great, YOINK!".
Eating chocolate renditionsThe most common example of this is the Chocolate Hitler. Every year, millions of people thank Hitler by eating a small chocolate sculpture of him. Little does he know, they wouldn't care if they were eating a chocolate molded Easter Bunny, as long as it tasted the same.
Cutting off an ear
A big hit with the ladies. If Van Gogh can, then why not eh? And for all those who are as straight as lightbulbs, Men prefer sacrificing toes.
Writing a Biography
Rather than copying someone directly a biographer will write down everything someone else does, thereby creating an instruction manual of copiable actions for a third party. Biographers thus abet a number of indirect plagiarists without committing the act of plagiarism themselves.
Writing a Top Ten Charting Song
To save oneself from the amount of work necessary to create a biography, they can instead choose to write a song about the person. The overall context of the lyrics may be filled with obsessive loathing or desire, so long as it is within good taste. Finally, in order to achieve top ten status, a catchy riff or verse must play repeatedly throughout the track, thus reminding the world that your subject's nose hairs make for the most wondrous artificial eye lashes or something along those lines.
Commission the rendering of a striking visage of the subject, on no other than the finest and softest of jet black velvet available. Highlighting in metallic and/or pastel colors is preferred as those will dazzle under the blacklight used to illuminate the painting.
What more sincere form of flattery is there than tracking every detail of the life and activities of your object of adoration, so that you can steal their name and peel off their perfect skin to wear during sex? I posit that there is none. (Stalking is for creepers. - Madi)
This is almost as sincere as stalking, but is a lot less work and doesn't require you to leave the keyboard.
Claim that God hates them
This demonstrates your acceptance of them as a threat to your pitiful way of life. Don't worry - nobody will take you seriously although some people may be convinced that they are not required for use as a sunbeam.
As long as The Beatles' "In My Life" is on there, this will prove your adoration of anything to anyone.
By eating someones heart, you're saying "Hey, I want to be more like you, and I want to steal your rich, tasty courage." and that is quite flattering. It is also recommended to store the person's head in your freezer, where you can forever gaze on his/her majesty while you grab some ice cream or a cold one.
It just seems to fit in with the others.