Delicious bus metaphors

I like expressions that don't make a lot of sense but kind of do.  Like "to throw someone under the bus".  We all know what that means, one person was a dick and fucked over someone else.  But what does that mean? I guess I get it.  I mean, if someone threw me under a bus, that would suck.  I would be run over by a bus.  That would be bad.  Buses are big and heavy.  An unfortunate place for me to be thrown would be underneath one. 


Another great one is "you can't have your cake and eat it too".  I have no idea what that means, but if I really think about it, yeah, I'd love to have some cake but also get to eat it.  It's like having two cakes. that would be awesome.  And yes I can see why I can't do that, most of the time, I've only got one cake.  Perhaps it can be summed up by saying, "You can't have something and also not have that thing.  In this instance, that thing will be cake."