It's up to the rest of you to change topic. One person shouldn't be driving the conversation unless the rest are responding. Maybe speak with the first few peop

It's up to the rest of you to change topic. One person shouldn't be driving the conversation unless the rest are responding. Maybe speak with the first few people that joined your lunch group, hint that you preferred it when lunch was a break from work related talk. If the others are ready to change topic, the gossip will die off and the gossiper will learn it's a conversation killer. If he is determined to gossip during lunch he will remove himself from the group - you get your lunch group back to enjoy.