Things that brake cleaner can ruin:

1. Some wood finishes
2. Clear plastic magazines like 10/22 banana mags (found this one out the hard way)
3. Some older plastics made in the pre-polymer era
4. Some rubber components
5. The glue that holds on Talon grips (another one I found out the hard way)
6. brain cells (make sure to always use it in a well-ventilated area)

And honorable mention: If you cut yourself and put on a Band-Aid prior to your cleaning session, not only will it take the Band-Aid off but it will hurt like Hell in a hot summer when it gets into the wound. Yet something else I learned the hard way.