Letting your swear down

"Some Christians will only swear around other Christians."
". . . ?"
"That way they don't have to worry about ruining their witness."
"Except, you know, because of their total hypocrisy."
"It's like letting their hair down."
"Letting their swear down?"

Something like this conversation occurred in my small group one day.  I was 100% flabbergasted (and horrified).  How about you?  Do you know people like this?  Can you explain to me why they think this is okay?  I'm quite curious . . .