The original Gary Larson cartoon dog (on the right) looked a lot like a long-backed Bouvier to me. So I re-drew him as a Bouv and changed the owner's sentiments to those likely to be expressed by a well known Schutzhund competitor of the era. (I'm not going to say just who I had in mind, but others competing in that era can probably guess.)
 
Revisiting these cartoons today I am struck by what really BAD advice the dog's owner is giving to the visiting guests. By counseling them to put one hand accross their throats, he is surely ensuring that they will be afraid of the dog. The advice to put one hand confidently down onto the dog's head is absolutely terrible advice : many dogs view a hand coming down towards their head as a threat and will react with fear, either retreating or with self-defensive aggression. This dog is already in a mood of fearful aggressiveness, and it would not take much more to get him to bite. Notice that the dog's body is leaning slightly backwards, indicating some uncertaintly or fear. Notice that the corner of his mouth is somewhat backwards indicating fearfulness, while the lip above his canines is lifted indicating a threat directed towards the cause of that fear. This whole situation has a high risk of a BITE and the owner's advice is raising that risk considerably.
 
So what would be better advice ?
First of all the dog should be on a leash and preferably with a halter on his head, and probably he should also be muzzled. The visitors should be asked to "Stand sideways to the dog and do not make direct eye contact and do not try to touch the dog." That's assuming the visitors are very dog-savvy. Ideally the visitors would have come provided with delicious food treats to drop to the floor in front of the dog with a minimum of hand and arm motion. (The owners could have placed a container of treats outside the door and given the visitors instructions prior to the visit if this visit was arranged for purposes of training the dog.)
If the visitors are not dog-people, then it would be better to avoid any problems by having the dog crated and let visitors perhaps toss some delicious treats into the dog's crate, again with their body posture sideways and avoiding direct eye contact.
 
By the way,notice that the original Larson dog also has the corner of his lips drawn back indicating submission or a bit of fear and has his tail at half-mast which likely indicates some lack of confidence. The hackles on his back are a bit raised, indicating a bit of arousal. While this dog is not as primed to bite as my version, I would not be real quick to reach down towards his head. I really dislike getting biten and I hate for dogs to have chance to learn that biting is an effective way to make a threat retreat.