Context

This line is from the song "Don't Be Cruel" by Elvis Presley (1956).

When Elvis Presley, the King of Rock and Roll, wasn't gyrating his hips on TV and being Elvis "The Pelvis," he crooned sensitive love songs. These became number one smash hits in a world where music had to be bought on vinyl and the word "download" hadn't been invented yet.

The refrain for "Don't be cruel" is, unsurprisingly, "Don't be cruel to a heart that's true." Elvis is telling you his heart is true, he doesn't want no other love, and baby, it's just you he's thinking of. Aw, shucks.

Where you've heard it

This song was one of the biggest hits of Elvis's career.  If you're chatting with an Elvis impersonator, they'll likely speak in only in catchphrases like, "don't be cruel" or "thank you, thank you very much" in between bites of fried peanut butter, bacon, and banana sandwiches.

Oh, and for some reason, it was covered by Daffy Duck.

Pretentious Factor

If you were to drop this quote at a dinner party, would you get an in-unison "awww" or would everyone roll their eyes and never invite you back? Here it is, on a scale of 1-10.

You're a lover, not a fighter, and there's nothing pretentious about that.