What is the things which are prohibited during fasting

A fasting person must not vitiate his fast and lose its reward. He must restrain himself, [both physically and mentally], from doing or thinking of anything that incurs the wrath of Allah Almighty and which make him forfeit his fast. These include:
Slander.
Talebearing.
Gossip.
Looking at what Allah has prohibited.
Quarrels and discord.
Severing the ties of kinship.
Abu Hurayra narrated that the prophet [pbuh] said: "It may be that a fasting person may not receive anything from his fast except hunger, and it may be that a person praying Qiyaam [Night vigil prayers] at night may not receive anything in recompense except staying up late" [Reported by al-Nisa`i, ibn Majah, and Ahmed. Ibn Khuzaimah, ibn Habban and al-Hakem declared it authentic].

Anything that eliminates or diminishes piety eliminates or diminishes rewards because fasting was legislated to attain piety. Allah Almighty says:
O you who believe! Fasting is prescribed to you as it was prescribed to those before you that you may (learn) self-restraint [Al-Baqarah, 183].
Allah Almighty knows best.