While fasting, it is important to not only abandon one's food and drink, but also to shun evil deeds. This includes false speech, backbiting, obscene behaviour, etc.
"Whosoever doesn't abstain from speaking falsely, and acting upon false speech, Allah does not care for his abstaining from eating and drinking." (Al Bukhari)
"Fasting is shield; so on a day that one is fasting, he should not indulge in offensive behaviour or arguing; if anyone verbally abuses him or provokes him, he should say: 'I am fasting.'" (Al Bukhari and Muslim)
