Expression used here and there by Everybody
"tonchinkan" means something like "doing something nonsense", "talking nonsense" • You use this expression when you want to say that something or someone is not being clear or is confusing. Also when someone is talking nonsense.
"本当に飛んでる馬を見かけたよ!" "なにとんちんかんなこと言ってるの?"
"I swear I saw a flying horse!" "Stop saying something so tonchinkan!"