How to deal with crazy teachers

Most crazy teachers, when you look at them closely, are really not that crazy. Unfortunately, that level is often impossible for students, at least, to find. Therefore, you're probably going to have to deal with them as is- which is going to require some specialised techniques.

The important thing is about communication, because, to be fair, they probably think that you're crazy as well. You need to stick to simple language and short sentences. This makes it much harder for what you're saying to be misunderstood or misinterpreted (although keep in mind that crazy teachers have been known to manage anyway, generally in ways other people never even dreamed of.).
Body language must be kept as open and unthreatening as possible. Imagine if you were constantly surrounded by loud, probably obnoxious people you don't really understand, how would you feel? And especially keep in mind that you should attempt to look as truthful and earnest as possible.
Lastly, what you're actually saying to them. Repetition is generally considered to be key in dealing with crazy teachers. They need to hear an idea expressed, in several different ways, before they will even begin to accept its reality. Also, if your content is something along the lines of "I need to skip your class to go to the zoo," it will probably need to be altered for the benefit of the crazy teacher. For example, phrasing it as "I'm representing the school to the general public, as part of a program studying the psychological similarities between humans and animals," may be more successful than "I'm going to the zoo." (no joke, my friends actually went on a psychology excursion to the zoo for that purpose. Or rather, that's what their teacher told the school- really, she just wanted to take them to the zoo. Gotta love that kind of crazy)

Furthermore, you will need to attempt to understand the mind of the crazy person. Don't worry- it's not as scary as you think it will be. They generally have one or two motives driving them- usually their subject is one of them. We have two especially crazy teachers at my school. One is crazy for her language. The other for his subject (geography, I'm pretty sure) and his school faction. Armed with the knowledge of what motivates your crazy teacher, you can manipulate their psyche. For example, instead of saying "my science teacher is taking us on an excursion to eat sushi as an end of year party thing" phrase it to a language teacher as "My teacher wants to help facilitate inter-racial understandings. We're going to develop cross-cultural bonds here!"

However, eventually, you are going to have to admit defeat. Some craziness simply can't be dealt with. You here have two options. Simply skip the class in question, or refuse to do the specified activity, or whatever. That's called wagging, though, don't do it. Or, you can do the far simpler option, and simply handball the whole issue to another teacher. Even if they can't make the crazy one see sense, they at least have the authority to let you do whatever it is you need to do.

And the last issue in dealing with crazy teachers? Yeah, sometimes, it is you, and the teacher you're calling crazy is completely rational and just trying to do their job while you, however, are being a shitthead. Which is it?

(Side note: we've apparently had FIVE fire alarms in the past two weeks. I haven't heard any of these. That's... encouraging.)