I actually missed the 'elbow' as I went out for a split second, but looking back on it it was nowhere near as bad as was made out. It wasn't even an elbow, he pushed him away with his forearm. Even funnier was that when Pjanic turned away reeling in imaginary pain he was then flattened by Gervinho, which made it look even worse.
Obviously I've seen players getting reds for less, and his arms was too high, but Chiellini wasn't even looking at Pjanic.