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					Originally Posted by concretegurl  Try a neutral area.
 My Scoobers is super friendly...hiwever there is a certain type of person who will cause the same reaction from him.
 
 My friends dog has only one person she doesnt like she will snarl growl and snap if he attempts to pet her...she was this way from day 1 with him.
 
 Trust your dog if its only with him there's a specific reason.
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  I would agree with this post and another on here.  
The one thing I was thinking of does this male wear a hat or sunglasses, when they stop by?  Some dogs do not like either attire.  
This is an awkward situation, especially if your dog only has done this with one person.  I would file that info away in my minds' memory.  But in future would as someone else suggested, crate the dog for now, while this person enters.   Let them out after everyone has settled down with a cup of tea/coffee, whatever.   
If your dog acts aggressively to this male, who has been brought into your home and is being treated as a friend.  Correct behaviour and crate dog.  
It is a fine balance you walk, but basically in your home, and with your dog, you as Theresa said are their Protector, Leader, Provider.  Your dog can not usurp that place.  And should not be allowed to.   
How-ever I do believe in and honor my dog's instincts.  For me unless some other evidence comes to the forefront, I think I would always have a bit of wariness about a person my dog took a disliking to.  
As humans many of us get some warning sense too.  Sometimes we over-ride it, but it truly rarely goes.  There are good reasons for this.