It'd be 'Siddhartha fucking Buddha' if we're talking about the Buddha. There are other Buddhas whose moniker you could use (e.g. Amithaba), and Siddhartha Gauta

It'd be 'Siddhartha fucking Buddha' if we're talking about the Buddha. There are other Buddhas whose moniker you could use (e.g. Amithaba), and Siddhartha Gautama had other monikers (Shakyamuni Buddha), so variations would be possible. As for the stance on blasphemy, I'm not certain but I expect it may differ between sects.