This is a nerd joke. It will make my daughter laugh. She likes to laugh at my nerdiness. I don't mind, because we both know she has inherited a lot from me and she can't deny it.
I admire people who are naturally funny, or who are willing to put in the effort to be humorous. Those people make a real contribution to the world by increasing the amount of laughter and smiles.
I'm not naturally funny, and I'm usually not willing to try. But I do see the humor in everyday situations, and sometimes I'm able to point it out when other people have missed it. My specialty is knowing how to make a particular person laugh. The secret is in referring back to a previous remark or situation. That's partly what makes it easy to make my husband or my daughter laugh, because I know what they are thinking most of the time, and I remember so many things they have said or done.
My daughter likes to communicate through "instant messages." She is very conscientious about using correct punctuation and spelling, and almost never says ROTFL or IMHO. But she does use one shortcut a lot. Instead of "love" or even "heart" she types "<3". So the joke is, whenever I'm seeing her off at the airport or she's leaving with friends for a night out, I will say "less than three! less than three!"
I warned you.