A lot of people mistake meanness for honesty. As in "You're already fat. Wearing orange just makes it worse. You look like a short fat pumpkin." No one has said that to me but I've certainly heard it enough. It goes along with, "You're barely literate enough to write your own name. What makes you think you could write a book?" Again, not something that's been said to me.
It would be so much nicer, and just as honest to say, "I like the way you look in red. It really brings out the colour of your eyes." or "There's a great writing course being offered at the community college. At the very least you could make some good connections there." Wait a minute, I have heard the latter. Hmmm.
Rude is not a necessary component for honesty. It's not manipulation to make someone feel good about accepting your opinion. I like bold up-front characters who can be counted on to tell the truth. They call a spade a spade. (I usually call it a shovel but that may be a regional thing.) They're colourful, dynamic characters who really liven a piece up.
How one shares their opinion is one of the many little clues to people's personality. If your character is "painfully honest" be careful with that. Those are difficult people to be around over a long period of time. There's an edge to them that should manifest in other ways. I was toying with giving that trait to one of my characters but hesitate because it's uncomfortable for me to write harsh edicts - which is why I should do it.
Writing outside my comfort zone might make the community college writing course unnecessary.