Can I be sued...do they have a case?

Three and a half years ago a "friend" of the family loaned me a lawn mower to cut my lawn, he told me to leave it in my driveway when I was done using it & he'd pick it up the fallowing morning. The next morning I left for work and the lawn mower was still there, not 15 minutes later he showed up at my job with a big grin on his face as asking me if I had home owners insurance, I said why and he said his lawn mower was not there when he stopped by to pick it & claimed it was stolen, he was acting very suspicious...smiling and not at all like someone who just had there lawn mower stolen. Since he was a "friend" of the family and we felt bad for him we each gave him some money to replace the lawn mower which he gladly accepted however we never thought to get it in writing (I did not put in a claim on my home owners & he did not make a police report) He recently showed up at my house (3 & a half years later mind you) demanding I give him more money for the mower and if I didn't give it to him he would take me to court. Can I be sued? Would an attorney or even a clerk at the courthouse even accept his claim?