That would be no problem for OP I'd be happy to write them back. It's not infringing if you're not doing any business.

This is commonly believed, but is not actually true. Not generating revenue via the infringing activity might contribute to an argument of Fair Use, but it's not a magic wand that disappears copyright claims.

Copyright infringement is totally different from trademark infringement. Please re-read the thread.

They're not using Tinder's marks nor providing a confusingly similar brand.

Unless they copied art from Tinder, they are light years away from infringing on anyone's copyright, so I'd be even more happy to respond to those claims.

Tell that to Nintendo

and not to forget the patent lawyer for "swiping gesture" patent claim that will hit

sorry... i made an app like "the swiping app"...