As if a girl open up her breast in front of other girl and allow her close best friend to touched her breast?? It is halal or haraam?
It is permissible for a woman to see and touch the breasts of fellow women (excluding non-Muslim women), provided it is not with intention of lust. The awrah of a woman in front of another woman, is her private parts (vulva and anus) or the area between navel and knees according to Sunnis.
Breasts are "zeenah" (beauty or charms) of a woman which she can expose in front of Muslim women according to the following verse of Quran :
"And tell the believing women to lower their glances and guard their private parts and not expose their beauty except only that which is apparent and to wrap [a portion of] their headcovers over their chests and not expose their beauty except to their husbands, their fathers, their husbands’ fathers, their sons, their husbands’ sons, their brothers, their brothers’ sons, their sisters’ sons, their women, that which their right hands possess, or those male attendants having no physical desire, or children who are not yet aware of the private aspects of women. And they should not strike their feet, drawing attention to their hidden charms. And turn to Allāh in repentance, all of you, O Believers, that you might succeed." [Sura an-Nur 24:31]