I'm going out to see a man about a dog...

[tgeezer]

That is the problem, I understood that, การ+ a noun, meant the business of the noun, การเมือง >the business of the country, so การบ้าน >the business of the house. I lacked the experience of Thai schooling and later discovered that it was used to say ‘homework’. 

Obviously your wife doesn’t hear ‘homework’ because ‘homework’ is done at home and not done by adults. If it works then, she sees การบ้าน as something to do with another house I suppose. 

I like that because it shows that you are not slavishly following En-Thai dictionaries.  

I have been looking in Longdoo.com and *‘think’ I found การบ้านกานเรือน for politics as well and การเรือน being used for housework.

 

* Can’t be sure as Capt. Haddock as pointed out. 

[CaptHaddock]

When the English speaker responds to his wife's question of where he is going with, "I have to see a man about a dog," he is pointedly refusing to answer the question in a way that will be understood by the questioner.  He is not trying to mislead her. 

 

A Thai would achieve the same effect by replying, "จะไปข้างนอก."