I am sorry to confuse you, but the character's name is not John. In terms of confidentiality (for my work), I used a different name in the context I gave you, just in case. The name is neither John, Joe, Sam, nor Tom.
It is very interesting that there are many phrases using "uncle", some of which you show I do not find in my dictionary (like "Uncle Tomahawk"!).
With regard to Mr. Pedantic's comment, I' ll add another context. In the previous night when they were in bed, the character who wanted to make up with his wife asked her whether she wanted to have sex (of course she refused). So, I suppose he says "Uncle *** is here" to express he does not have ulterior motives. Also, now he knows that his wife wants him not to take the accessory as just a tool to make up, and he wants to show his generosity.
Thank you for your help and additional "uncle" phrases!!
Regards,
Gonta