sarcastic coughing fit
When a cough is used to indicate you think the exact opposite of what you just said, often the cough can be used to disguise saying what you actually think.
Example:
1. Yes, I'm sure you don't fancy him (sarcastic coughing fit)
2. Yes, he made the first move *cough* you so came onto him *cough*
1. Yes, I'm sure you don't fancy him (sarcastic coughing fit)
2. Yes, he made the first move *cough* you so came onto him *cough*