Because Hondo is a big boy, people get nervous if he spends a lot of time sniffing on them. If allowed, he'll sniff feet, legs, arms, butts etc. and take his time doing it. I don't want to give him a command that might make the person even more nervous. Say, if I were to say, 'Leave it' or 'Quit'. So I created, "Hondo (that gets his attention) that's rude!" The tone for 'that's rude' is the same tone as 'leave it'.
In the beginning when given the command, if Hondo continued to sniff, I'd remove him and make him lay down and stay by me. Like a time out. This also gives Hondo a chance to disengage from the new person. When I released him he'd go search for something else to do. Sometimes, he'd just get up and move to another area to lay down.
Now, I just say "Hondo, that's rude!" and he'll stop and go lay down.
Hondo Von Dopplet L Bauernhof "Hondo"- GSD
Lilie's Tug McGraw "Tug" - Golden Retriever
Maggie - Mini Dachshund (Rescue)
Lonestar Pivo - Texas Blue Lacy
Ashe - Barn Cat
Katie / APHA