fantastically shitty. combines excellent and excrement.
like if your boss has a low-end vocabulary and suggests that you work your day off in a way that you know you can't refuse you can give him a big smile and say, "Excrellent! I'll be here Saturday at 7am!" and if he even hears that you aren't saying excellent he will just think it's like all those other words he hears that he doesn't know and he'll infer from your smile and body language that it's something good. but really it isn't. and you keep your job too.