A local Jewish court in the community he lives in CAN excommunicate (in hebrew we call it cherem) him and that means he will not be counted as part of minyan (10 for prayer) and will not be invited to the synagogue and will be shunned by Jews who adhere to that court. These things had been done before (I don't mean back in the days of sanhedrin but even to this day) although rarely and not always justifiably, but it can be done.
Just fasting on Ramaden, alone, should NOT be grounds for expulsion, but actively seeking the destruction of Israel and the Jewish people should be. IMO, any person who actively seeks the destruction of the Jewish people and Nation of Israel , as well as actively aids and helps the enemy that has murdered and harmed Jewish people is a traitor and has no part of the Jewish people. He, IMO, as ChaimFan wrote earlier is worthy of the title "Cut Off From Your People".
Jacob Rosenblum, the Palestinian Nationalist, Anti-Israel, BDS Zealot is, IMO, worthy of such a title, as well as the Judenratt who helped Hitler round up Jews for the gas chambers, naively thinking they would be spared the same fate by complying. Neturei Karta, also, IMO, are worthy of this punishment, as they have denied the Holocaust and have worked to fight against Israel and support the worst enemies of the Jewish people. Many of the worst Anti-Semites use their Anti-Israel/Holocaust Denial protest pictures as some of their main propaganda, to try to prove that the evils of Zionism and Israel and how "Real Jews" are not suppose to support it.
However, this is my opinion and I am sure some will disagree.
Trying to "Co-Exist" with the enemy and be friendly I think is foolish, but not worthy of being ex-communicated or being stripped of your Jewish identity or thrown out of your Jewish community.