When you think about it, it's not even a big ask. You don't need to put time aside to do it, it doesn't cost you anything and it probably makes you feel a bit happier for making a difference to someone.
New homework guys, (I hope you've been enjoying the 10 minutes to yourself one, a la that Twinings campaign). I want you (even for just one week) to compliment someone or say something positive to someone every day for the rest of this week. It can be either someone you know or a stranger but the important thing is that you've made an unexpected difference to their day.