Hazrat Mufti Ebrahim Salejee (Daamat Barakaatuhu) mentioned:
To taunt a person regarding a sin for which he has already made taubah is extremely disliked and dangerous. What gives one the right to taunt such a person? The hadeeth says that Allah Ta‘ala will make it such that the one taunting will not die unless he also gets involved in that sin. The problem was between him and Allah Ta‘ala, so why must we get involved in his matter.