My favourite false cognate is the plural ending -s in French and English. The English one has Germanic roots, while the French one come from Latin accusative plural -as/-os. They are unrelated etymologically.
I'm used to the dot from all programming languages. And also the comma interferes with the CSV (comma separated values) file format.
For the thousands separator, my favourite is the apostrophe.
An office chair. A piece was wrong making the thing unassemblable. Got the money back and bought a more expensive one from a much better shop. Happy about that because the expesive chair is much better than what the cheap one would have been.
If ^L is invisible in your editor, you're using a bad editor.
Not saying page feeds are useful, but you can't complain that you don't see them.