http://www.alt-usage-english.org/ucle/ucle9.html

"Bloody" "Walk! Not bloody likely. I am going in a taxi" (Liza, in George Bernard Shaw's 'Pygmalion', 1914)

"…[English]… is taught so bloody badly…" (Prince Charles, 1989)

"I never use the word 'bloody' because it is unparliamentary. It is a word I never bloody well use." (MP, 1980)

The use of "bloody" as an excessive adjective apparently entered our language about 300 years ago. Folk etymology has it that it is a euphemism for "by our lady". The logic of this etymology, however, fails in the translation of meaning and intent from an oath ("by our lady") to an intensive adjective ("bloody"). For example, to say "it's by our lady cold outside", "by our lady hell" doesn't really make sense, even though Jonathan Swift attempted it.

A more satisfying explanation is that it describes a state of bellicose drunkenness: it is natural that someone in a drunken state who was eager to fight would have a flushed face; and hence, "bloody drunk". A parallel, and equally satisfying, explanation is that it comes from the term "Bloods" as used to describe young and arrogant aristocrats.

Its use as an integrated adjective seems to be from the 20th century. Examples of "bloody" as an integrated adjective are: "Not bloody likely", "Abso-bloody-lutely", and the Australian "Kanga-bloody-roo". There is little doubt that the Aussies hold all known records for the use of "bloody" as an enclitic device.

"Ruddy" and "blooming" are thought to be derived as euphemisms of "bloody".