Calling String Bets: Rude?

[TrvChBoy]

At the home games I play in, we are very quick to call "string bet" on someone who has made one. Often it will be someone who is not even in the hand. We don't have a dedicated dealer.

When watching High Stakes Poker recently, I heard Gabe Kaplan state that the players were very reluctant to call "string bet" on another player.

Is it rude? We want to play by standard rules at our home game, but we don't want to encourage behaviour that would be rude at a B&M.