"Make no mistake," Megatron replies, "I am no less displeased with the choices you have made. However..." He glances over his shoulder, at the gathering of Earth heroes. "...This is far from the appropriate venue for the airing of such grievances."

He might have gotten just a little carried away over the last couple of hours. He has spent a while talking himself up to real humans as an intimidating and dark arbiter of justice in his fabricated Earth city of origin and their reactions have on the whole been pleasing. He has been... enjoying himself. He may have allowed an interested child to touch one of his arm spikes. Objectively the whole thing would be kind of embarrassing and generally unacceptable, but the individual he is presenting himself as here is not Megatron, and therefore it is not his own reputation that's at stake here.