infixation

Yes, but I do not. I use -fixation in a morphological context. To my mind, something different is going on with the abso-bloody-lutely type phenomena. What gets infixed is a morph (cf. nasal presents in Greek and Sanskrit), not an independent word. What's going in in (modern) tmesis seems more like a rhetorical device than a morphological process. But, hey, that's just me!

Ceci n'est pas un seing.