Regardless, literally everything I've ever seen (and a lot on tfwiki) attributes Megatron's slide into violence to Whirl beating him up while in custody. Maybe not like flicking a switch but Megatron's line "You made me. You taught me words were weightless without force" kinda spells it out.
So hey I bought Triggerhappy from Walmart a few days ago and just notice the receipt said TRIGGERHAPPY on it. Not the assortment name or whatever. Are they using this info to better track character sales or something?