Bismellahi Irrahmani Irraheem
Want to stop?
Say : "My Lord! I seek refuge with You from the whisperings (suggestions) of the Shayatin (devils) and I seek refuge with You, My Lord! lest they may attend (or come near) me." then forgive that person just for the sake of Allah and make Du`aa for him/her to hit the head and step on the nose of satan; who wants to fill our hearts with hate and take us away from Allah and the mercy which He planted in our hearts for His creation...(A`othobellah)...
and always remember that Allah says:
"The good deed and the evil deed cannot be equal. Repel (the evil) with one which is better (i.e. Allah ordered the faithful believers to be patient at the time of anger, and to excuse those who treat them badly), then verily! he, between whom and you there was enmity, (will become) as though he was a close friend. (34) But none is granted it (the above quality) except those who are patient, and none is granted it except the owner of the great portion (of the happiness in the Hereafter i.e. Paradise and in this world of a high moral character). (35) And if an evil whisper from Shaitan (Satan) tries to turn you away (O Muhammad SAW) (from doing good, etc.), then seek refuge in Allah. Verily, He is the All-Hearer, the All-Knower. (36) " Surat Fus`silat
and says Ta`aalaa:
"And march forth in the way (which leads to) forgiveness from your Lord, and for Paradise as wide as are the heavens and the earth, prepared for Al-Muttaqun (the pious - see V. 2:2). (133) Those who spend [in Allah's Cause - deeds of charity, alms, etc.] in prosperity and in adversity, who repress anger, and who pardon men; verily, Allah loves Al-Muhsinun (the good-doers). (134) " Surat Aal`imraan
trust Allah no matter what in everything and seek Allah`s help , support and guidance and you will never ever regret it...(Allah Is your cure)...
return to Qur`aan and Sunnah in shaa Allah and you will find many ways to remove your anger which causing that bad feeling ...
I believe that as long as you are asking how to stop having that bad feeling for that person then what you have in your heart is not hate and you didn`t reach that level yet in shaa Allah,May Allah protect you Ameeen but you are only mad of that person too much...May Allah be with you Ameeeen...
May Allah help you be with you and fill your heart with Iman Taqwa His rememberance love peace warmth the endless happiness and satisfaction and ease everything for you opening all the doors of goodness and success for you and guiding your way to the path of Al Jannah...Ameeeen...
take care of your self...
leaving you under Allah`s sight care and protection...
with all my respect and humility...your sister...