… well, most people know how that epithet ends with a NSFW word. If you don’t know how it ends, don’t worry about it and enjoy your day.
Let’s think about this phrase a moment and how people think karma works. Good karma comes to good people, bad karma comes to bad people; it’s a fairly simple ideal. Now, let’s expand on those basics a bit.
One should not be wishing bad karma on people because, well, that’s actually a bad thing and thus making you a target for bad karma, too. It’s much like pointing a finger at someone; you’re most likely pointing three fingers back at yourself.
Go ahead, try pointing a finger at the screen and take a look at the other fingers on that hand; where are they pointing to?
Telling people that “karma’s a biatch” (a little poetic license for effect; safer for work but you might have your kids asking questions) is fine; but, more often than not, when one person says it to another they’re usually just wishing bad karma on them.
Just another thing to consider when making wishes, although not intended for yourself they may be granted on you all the same.