Is one allowed to embarass a Gentile? I have heard about the severity of embarrassing a jew. Leaving aside the chances of Khillul Hashem, Is there any sin regarding the embarrassment of Gentiles?
As the question is a legitimate question, I hardly see a need to find an actual scenario whereby it wouldn't be prohibited as a Chilul Hashem.
Nevertheless; here are several scenarios which come to mind. A. Where the Gentile thinks that you are a Goy. B. Where you shame him anonymously (e.g. on-line, or yelled out in a crowded room, or flashing pictures that humiliate the Gentile, etc.
The severity of the sin of publicly humiliating another (Hamalbin pnei CHAVIROI b'rabim ein loi chelek b'oilem habuh) only applies to a fellow Jew; just like the commandment of loving your neighbor/friend as [you would to] yourself (v'uhavto L'REIECHU k'moichu) only applies to a fellow Jew.
Regardless, it is prohibited to cause suffering even to an animal; and a thousand fold worse to do so to another human being.
The Gemara writes מוטב לאדם שיפיל עצמו לתוך כבשן של אש ואל ילבין פני חבירו ברבים*.
Rabbeinu Yona explains that embarrassing another person is יהרוג ואל יעבור, because it is אבוזרייהו דשפיכת דמים. Accordingly, embarrassing a gentile would have the same status as killing a gentile.
[*The Gemara learns this from Tamar, who was willing to give up her life so as not to embarrass Yehuda. According to many opinions, Yehuda had the status of a Ben Noach. (See Perashas Derachim for in depth analysis of Yehuda's status, and the possible disagreement between Tamar and Yehuda in this area.)]