This article systematizes speech registers employed in in-law avoidance into a cross-linguistic typology. Such affinal avoidance registers, consisting of lexical repertoires substituting for “everyday” speech forms tabooed for certain speakers or in certain contexts, are shown to typically diverge from one another in terms of two parameters, their context-sensitivity and the relatively idiolectal or sociolectal character of their register repertoires. Comparative data illustrate that Aboriginal Australian “mother-in-law” speech registers, which are context-sensitive and exclusively sociolectal, are highly exceptional among affinal avoidance registers cross-linguistically. In the final section of the article I seek to understand this exceptionalism in terms of the broader context of Aboriginal Australian ethnolinguistics.