Is the clockspring missing or something?
I assume you checked the fuse for the horn. Of course if it IS bad, you will have to figure out why.
For the horns though - there isn't much to them on any car -
The horn, the relay, the switch in the steering wheel, associated connections. Is the horn wire connected properly?
Of course if nothing else, you can always use your middle finger to signal drivers that have cut you off. I mean it has the same effect but is visual instead of audible.