What's the most cringeworthy thing your dog does to embarrass you?
The dog addicted to crotch sniffing is right up there. For example, imagine your dog meets and greets your boss by gluing a nose to their crotch... not a great way to get a raise at work.
However, crotch sniffing is natural canine behavior. Your dog isn't trying to get you into trouble, merely wanting to find out more about a person. It just so happens that most people don't find a wet nose in the nether regions socially acceptable.
Of course, punishment is not an option. How would you feel if someone slapped you every time you smiled at a stranger? But this doesn't mean you have to accept crotch sniffing. Instead, you simply need to teach the dog an acceptable behavior to perform when they feel the need to sniff.
Success depends on consistency. For this, you need to prevent crotch sniffing while retraining (keep the dog on a short leash when close to people) and train regularly so that the dog gets the message.
Rather than 'stopping' one behavior (crotch sniffing) you teach the dog an alternative behavior (sniffing an open palm, looking at you, or going to a mat) that is acceptable. This keeps the dog active and thinking, hence distracting them from their chosen activity.
Ideally, start young by training a puppy. It is far preferable to start with good habits than stop bad behavior once it's developed. However, we don't live in an ideal world and sometimes it is necessary to retrain an adult dog. This is perfectly possible but be prepared to train regularly, twice a day for 10- 15 minutes at a time.
Depending on your chosen method, you'll need a combination of the following items: