Expletive infixation is a process by which an expletive or profanity is inserted into a word, usually for intensification. It is similar to tmesis, but not all instances are covered by the usual definition of tmesis because the words are not necessarily compounds.
The most commonly inserted English expletives are adjectival: either participles (fucking, mother-fucking, freaking, blooming, bleeding, damned, wretched) or adjectives (bloody).
Rules of formation in English
Judgments of which formations of expletive infixation are acceptable are remarkably consistent. This suggests that the rules for the placement of the expletive are not arbitrary, but instead derive from fundamental aspects of English phonology.
A simple rule is that the insertion occurs at a syllable boundary, usually just before the primary stressed syllable.
A more fundamental theory due to John McCarthy is based on prosody.