Curious greeting ritual: Why dogs like to sniff people's crotch. If a dog smells a person's crotch, it may become unpleasant.
From the four-legged friend's point of view, however, sniffing should be interpreted as pure interest. You should only interpret a surprise attack on the intimate area as a greeting or introduction. If you are aware of your dog's intrusive behavior, you can help yourself by putting the dog on a leash. You can get tips and tricks from your trusted veterinarian, dog trainer or school.