"you drank their acid and concealed it." - meaning people bullied you, and all you did was keep it bottled up inside. You never shared it with anyone and it was like acid eating away at something, all the people were slowly weakening you. "If you faced the death of bombs and bullets you did not do it with a banner, you did it with only a hat to cover your heart." - I think these lines means that if you had problems or troubles, you faced them alone. Once you overcame them you did not brag about it or gloat, you protected yourself from the humility. "You did not fondle the weakness inside of you though it was there." - meaning that even though you had a great deal of weakness and fear it was kept inside of you where no one could know or find out how much you had. "If you have endured a great despair, then you did it alone." - After you have went through a hard time, alone and with no support, you have got stronger every time you have done overcome something.