I'm going to tell someone to not be so bitter on valentine's day
Why would you want to tell someone not to be bitter?
I want them to know I don't care about Valentine's Day.
If they are not in a relationship they may feel bad about the day, that's understandable. You can't make someone feel the way you want them to.
Let others feel bad about that day. My friend should get over it.
It's not fair to expect only your friend to get over it. You need to have more empathy for them.