Infuckingfixing.

Neil Gaiman has a most delightful blog, in which he relates things he has learned and by which we can learn them too. It turns out that words like "absofuckinglutely" have a grand linguistic heritage.

An infix is an affix inserted inside another morpheme. This is common in Austronesian and Austroasiatic languages. For example, the Tagalog language has borrowed the English word graduate as a verb. In this language, a grammatical form similar to the active voice is formed by adding the infix to the first syllable of a verb, so a speaker saying "I graduated" uses the derived form grumaduate.

It's called "infixing." When Snoop Dogg says "hizouse" and "shiznit," he is also infixing. There's a special entry for expletive infixation with many delightful examples. Fanfuckingtastic.