Categorise the bad dancer
There are various types of bad dancers and you need to categorise while dancing. Some people are extremely bad but they are over-confident and assume that no one dances better than them. Whereas, most of the bad dancers know that they are not good at dancing but they keep trying. You can be a little rude to the first category but always be gentle and polite with the bad dancers of the latter kind.
Once you categorise the type of a bad dancer, you will be in a much better position to drive the dance moves.
Make him feel comfortable
If you have chosen a person to dance with and he is not up to the mark, you need to make him feel comfortable with you. If you express your disappointment, the other person is likely to get confused. Have a little chat with him and motivate him. Once he becomes comfortable and starts to dance with you, he is likely to improve with the passage of time.
Give him/her hints
If your partner is not a good dancer, you will get to know that within the first couple of moves. In such a scenario, keep eye-contact with your partner and give him/her some hints. You can even teach him/her some basic dance moves quickly in order to prevent embarrassment.
Enjoy the situation
Instead of getting frustrated by the situation and spoiling your mood, it is highly recommended that you see the fun part in dancing with someone who is bad at it. You should take this situation positively and think as if it is a test of your leadership skills.