Loose lips sink ships, and that's exactly what this person specializes in. They might be trustworthy with your pet or child, but forget about telling them anything top secret — it's bound to come out, whether they realize it before it leaves their mouth or not. Instead of managing the conversation so nothing juicy or otherwise unknown gets out (isn't that the fun part of dinner parties?), leave the big mouth off your list. After all, what happens around the dinner table stays at the dinner table, right?