Résumé : Negation is intrinsic to human thinking and most of the time when searching for something, we base our patterns on both positive and negative conditions. In a recent work, the notion of term was extended to the one of anti-term, i.e. terms that may contain complement symbols. Here we generalize the syntactic anti-pattern matching to anti-pattern matching modulo an arbitrary equational theory E, and we study the specific and practically very useful case of associativity, possibly with a unity (AU). To this end, based on the syntacticness of associativity, we present a rule-based associative matching algorithm, and we extend it to AU. This algorithm is then used to solve AU anti-pattern matching problems. This allows us to be generic enough so that for instance, the AllDiff standard predicate of constraint programming becomes simply expressible in this framework. AU anti-patterns are implemented in the Tom language and we show some examples of their usage.