I need to tell my boss that my colleague is ratting on her

my colleague is a real kiss ass, he is keeping tabs on my boss whenever she's late or whenever she works from home (which she is allowed to do!) and writing down stuff she says, all with the intent take it to our higher boss. My boss is absolutely amazing she's so understanding when it comes to our lateness, sickness etc and never makes us feel awkward for it. I have worked in offices for 5 years, my colleague is fresh out of university and thinks because he has a degree he is entitled to a managers position straight away and clearly thinks the best way to do it is to ass kiss and rat on our boss for being late a few times and making a few jokes. I really want to tell her what he is trying to do but I don't know how to approach her without it seeming like I'M the snitch!? Please help. She doesn't deserve this.