Is it abrasive or unacceptable that Satya Sai, the famous Indian spiritual guru, proclaimed himself to be God?

no , because according to hindu scriptures it says every one is god , though it sounds like egoistic in real it is and true and its higher state of enlightenment , but its up to everyone to believe in this issue or not , but it is true , according to god theory everyone is god only possible way to know that is by doing severe austerity like sage , then only it is possible to realize that we are equal to god , due to this mundane we are surrounded by maya in which it wont let us to explore that .