In a game of Spirit of the Century, the DM had kitted out some of his forces with guns that fired syringes rather rapidly. At some point or another, we overpowered or killed a group that were weilding these. One of the party then grabbed one of the guns, and turned it against the bad guys. It was never adequately explained what was in the syringes, but when one of the bad guys was hit in the arm with about four of them, he started screaming and his arm hulked out. Like, seriously. It was almost bigger than him. He proceded to try and kill us, but we turned him away. He smashed a hole in a wall, jumped out of the second or third floor (I forget which, but high), landed on the giant arm, then started throwing himself across the landscape. The DM continues to threaten to bring "arm guy" back.
This was long before we found out about L4D2 with its very similar type of infected. XD