Here's a love song card you can buy on Etsy. It's only $4, because unnecessary quotation marks make everything feel cheap. "Trust us."
What do you think they meant by "The Sweetest Thing"? We at SPOGG hope they mean kittens, or maybe candy, because anything more personal should never be printed on a card.
Oh, and about the proper use of quotation marks: They belong around direct quotes and words you are referring to as words themselves. For example, the "sweetest thing" in that poem couldn't possibly be a reference to the ability to achieve an orgasm. No one would be that gross.
Quotation marks are not to be used to highlight the adorableness of certain expressions. Nor are they to be used to show that you're kidding or being clever. Your writing has to be funny enough to stand without the air quotes.