Haven't learned to say F U politely

Yeah, I'll clean this up a little.  Can't have people offended, not on the internet.
I've learned to bite my tongue over the years (those who work with me will disagree, I'm sure).  It's more of a political thing.
Be nice to the waitress so you don't have spit in your food.  That and maybe she's having a bad day and it will be easier to manipulate the situation by appearing sympathetic, and therefore endear her to you so you get better service.
Is that disingenuous?  Manipulative?  Yes.  But they are pretending to like me so they can get a tip, so that's okay.
Social media is more tricky.  You almost have to be friends with people on Facebook whom you work with.  Even if you don't like them, because if you don't you get the inevitable "why didn't you accept my friend request?".
To which in the real world I would answer, "Because I don't like you and wouldn't piss on your gums if your teeth were on fire." But* in which I have to respond with, "Oh I'm not really on there much.  I just use it to play games on." Or some other lie in order to not hear from my bosses "It doesn't matter if you like him, don't piss him off and do your job".
Twitter is even harder.  I don't want to respond rudely, these are potential customers and networking people.  If I offend them I could potentially hurt sales, or opportunity.
What to do?
I know some people get lots of followers by being rude.  I'm sure they lose out on a lot of chances, too.  I don't want to be a slave to a tip.  I want that tip, though!
So if I want authenticity I must be authentic.  I can still be polite and speak my mind.  Be tactful.  Just not say F@ck you.
Or "You are an idiot".
Or "I know people that smoke crack that make more sense than you."
Or "I'm not saying you don't know what you're talking about, but I don't know what you're talking about."
Or "Shut up you knob gobbling thunder c#nt".
Or "No one cares about your teen pregnancy, just shut up and deal with the consequences. Need help, ask. Otherwise toss off."
I've never said that last one.  Maybe one day.


*Do not start a sentence with the word "but".