Just discussing things we used to do as children/teens to get out of school/get given Calpol back when it was sugary.
I used to douse myself in talcum powder and put the thermometer on the radiator, then shuffle in weakly to my mum, who I can only assume was so tired of my dramatic fake illnesses that she used to vaguely entertain this.
My friend used to rub Vicks under her eyes.
I also faked an eye test because I wanted glasses like Jarvis Cocker until the clearly savvy eye lady made me cry by telling me if I couldn't see any of the letters they would have to put a special acid in my eyes... 
Tell me of your/your DC's best fake/exaggerated illnesses!