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Here is a dialogue between a 30-odd-year-old hostess her handsome 22-year-old male employee:
(Please edit the dialogue to make them sound like spoken by native English speakers)

Hostess: Let's have a dinner together when off duty today.

Employee: Sorry, I cannot go to dinner with you, I have something to do at home.

Hostess: I am your hostess. I don't think it is not proper for a hostess to ask her employee to company her to have a dinner.

Employee: I work for you, not sell myself to you (And then the handsome employee turned and took a French leave).
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Let's try again, Jobb:

Hostess: Let's have dinner together after we go off duty.

Employee: Sorry, I can't. I have something to do at home.

Hostess: I don't think it's improper for a hostess to ask an employee out to dinner.

Employee: I don't either, but I really don't think it's a wise idea.

(And then the handsome employee turns and leaves abruptly.)

That is a more realistic piece of dialogue, Jobb. And 'French leave' is affected.
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-- What are you doing after work? How about dinner with me?
-- Sorry, I don't think that's a good idea. Anyway, I've got other plans.
-- I don't see anything wrong with asking you to have dinner with me just because you work for me.
-- I may be your employee, but I'm not your boy-toy too! (And he turned and left.)
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Comments  
Here's what I would put: (things in brackets [] are optional)

Hostess: Let's have dinner [together] when you get off duty.

Employee: Sorry, I can't go to dinner with you, I have something to do at home.

Hostess: I'm your hostess. I don't think it's proper for a hostess to ask her employee to accompany her to dinner.

Employee: I work for you, not sell myself to you (And then the handsome employee turned and took a French leave).

This sounds better, although I'm not quite sure about the details of a "French" leaveEmotion: smile .
 Mister Micawber's reply was promoted to an answer.
I think MM's version sounds moderate.

French leave
n.
An informal, unannounced, or abrupt departure.
[ From the 18th-century French custom of leaving without saying good-bye to the host or hostess ]
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 CalifJim's reply was promoted to an answer.
I would like to explore this one a bit further, Jobb, because some things have been bothering me about this dialogue, and it is not the grammar or vocabulary choice, it is its communicative value, or lack thereof.

What urged me to correct your original was not so much those mechanical items, as that the social view-- that nowadays an offer from a young woman to a young man for a date, irrespective of their work relationship, should cause the man to overreact in such a fashion-- seems unrealistic. Therefore, even if we 'fix the grammar', it is still 'wrong' in that it is not likely to reflect an authentic dialogue. With the context we are given, the dialogue which leads into his remark does not warrant the young man's sudden ire. That is why, in my offering, I changed the employee's second turn so drastically.

What this has brought home to me is how often here at EF we pay too much attention to the niceties of stucture, and not enough to what is being communicated. In actual communications, the foreign language student seldom gets punched in the nose because of poor grammar, but more often for inappropriateness of interaction. If in the above dialogue, the employee were an ESL learner, the hostess might well wonder what in the world he was thinking of, because she was simply being sociable (at least from the extent of context presented).

By the way, I had forgotten to expand upon 'French leave'. I said that its use here was 'affected', but in fact that is not the problem-- rather, it is inappropriate. 'French leave' is a departure without the host knowing, a quiet leaving-out-the-back-door when does not wish to see the host or does not wish to pay one's bill. Turning on one's heels and walking away from a person in anger does not constitute French leave.