The original rhyme was Roses are red Violets are blue Sugar is sweet And so are you There are hundreds of variations, often printed in valentine cards, and also often humorous - for example: https://www.quora.com/What-are-some-roses-are-red-violets-are-blue-jokes I guess in this case you are asking about the last word specifically... is that right? There is a french word "beau", meaning beautiful, that is sometimes used in english to mean a boyfriend, or a boy you have a crush on. In American english they pronounce it "boo" and over time it has come to be spelled "boo" as well. Boo is used in other contexts - to express disapproval or as a thing to shout when you want to surprise someone and give them a fright, but that's not what it means in this example.

Yes, sir, you are my boss! :) haha. Thank you for your comments, sir.

I'd rather make it "you are the president and I am your boss" haha

It's a strange American distortion - the French would be belle for feminine lovely - how it ends up as 'boo' who can say!