How to Deal With a Guy Who Believes in Mermaids

One of Debra's friends believes in mermaids. She has been venting about it to me lately, and I have no idea what to do. Should I let her have her delusions or try to burst her bubble? That's from Miff with Mermaid Park. The second part is this person who you are talking about here. We won't make that mistake a ninth time.