Neither is really correct. The first one is definitely wrong.
You will sometimes hear the second one used, but it is a slang form.
The proper form is 'Don't pretend to be having a good time'.
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Don't be pretending having a good time. INCORRECT
Don't be pretending to have a good time. CORRECT. (It's not slang.)
Don't pretend to be having a good time. CORRECT
Eric Clapton song for your enjoyment: https://www.youtube.com/watch?v=x4ylS4vkfH8
November 9, 2017
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