Guys this thing keeps me disturbed n detracts me frm studies?

ok well i have always been a sensitive child.ppl say anything on ma face n i listen to it quietly.i have a gullible personality.ppl take advantage of this and hit me with various sorts of abuses.now the desk in ma cl has the seating capacity of 3 .the other day 2 were sittiong on it and i asked one of them to shift inside so that even i cud sit in but she retorted back v rudely and i cud not say anything to her and since then a m just thinking about it relentlessly.i can't study bcz of that.i want a situation wherein even i can retort at that manly girl.i want some peace of mind.y r ppl like taht.when m always so good to everyone.plz suggest me ways so that i can concentrate on ma studies.