in class who ALWAYS has to raise his hand and say something (ask a question, make a comment, correction, etc). Typically has a nerdy voice, and appears nervous. In the most extreme cases has absolutely no idea what he's talking about, or where he's going with his question/comment. The teacher's response to the offending 'Actually Guy' will be somewhere between dumbfound silence, or grasping at straws to respond and be nice. Some teachers won't tolerate such nonsense and will simply tell them to stop talking immediately, or more politely tell them to allow other people to 'participate' in class.
Another way to identify an Actually Guy is to take a close look at the classroom's response to him. If there's a large amount of stifled giggles, whispers or audible groans there's a good chance you have a loose Actually Guy sitting in your very classroom. If he does this more than twice per class period, it's a very dangerous one.
Man, what is that guy doing? Christ, it's another Actually Guy. He's embarrassing himself in front of the whole class. Even the teacher feels sorry for him! He really should just stop talking, this is getting painful to watch...