Things came to a head when a friend came round with her teenage daughter. They laughed as you rough-housed the dog, and the friend's daughter then wanted a go. You were secretly delighted, as the girl is wary of dogs and you thought it would do her self-confidence good. However, this backfired badly.
In a predictable way, the dog quickly became over excited and nipped at her arm. Unfortunately, the girl screamed and claimed the dog tried to bite. Her mother became irate and it took a deal of convincing on your part, that the dog meant no harm and was only playing.
Still, another time and another place, and things might have ended differently with a phone call to the police, so perhaps it is time to teach the dog to be gentle and not nip.
Re-educating an adult dog means you must be prepared to play act a bit, and yelp when the dog's teeth make contact with your skin, no matter how minor the incident. In addition, it helps to learn strategies for calm play and how to distract the dog out of trouble. All of this takes time, so if you have small children in the home or are worried about the dog's behavior then always seek the help of a certified dog behaviorist.
To aid the process you will need: