Ironhide doesn't always see optic to optic with Optimus Prime, despite their friendship. He's perhaps the more practical of the two, and more than a little trigger happy.
Sam Witwicky:"No! No! He's not a rodent, he's a chihuahua! This is my chihuahua! We love chihuahuas, don't we?"
Ironhide:"He's leaked lubricants all over my foot!"