jashkenas/coffee-script — pull request #2461 by almost (2012-07-25 13:36:37+00:00)
Title: Added _this and _super to reserved words list

If you use either of these words in your code you are asking for trouble. It will be nice if CoffeeScript does the 2-pass parser thing at some point so this isn't needed but for now this will reduce unexpected annoying things :)