How can I reheat coffee without imparting bad flavor?
It's not going to be nice to drink a day later, no matter what.  I'd use it in baking a chocolate cake or something like that instead, if you can't bear to throw it out. 

The problem is not just the reheating, which will further cook the coffee and affect flavour, but that it's been losing aroma and oxidizing for a day first.  If you're serving it to anyone you like even a little bit, serve them fresh coffee!!