Break fluid

Uhh, it is B-R-A-K-E fluid. Probably won't hurt the windshield, but will destroy the paint.

If this is just a one time thing I wouldn't worry about it, besides brake fluid would harm rubber more so than glass. If this is a recurring thing then you have to ask what is going on that you have brake fluid on your windshield.

Brake fluid can remove the cars paint!

Ed. Since when does brake fluid have abrasive? Not unless it is contaminated.