There was a teacher at our school who always cringed at squeaky chalk, it just set her teeth on edge. So on April Fools Day someone brought some clear, quick-drying glue in and we all coated the chalk with it - even went into the store cupboard and removed all the boxes of chalk except two and coated every stick in those two boxes with glue too.
We kept all the chalk hidden in our desks, drying, until she was due to teach us. (This was in the days, you understand, when the pupils stayed put and the teachers moved around from classroom to classroom, not the other way round as they do today.)
It worked a treat, every stick squeaking away like crazy. Great fun!