This paper presents a corpus-based study of constructions in English and Spanish, with a special emphasis on equivalent semantic-functional counterparts, and potential mismatches. Although usage/corpus-based Construction Grammar (CxG) has attracted much attention in recent years, most studies have dealt exclusively with monolingual constructions. In this paper we will focus on two constructions that represent conventional ways to express ‘insanity’ in both languages. The analysis will cover grammatical, semantic and informative aspects in order to establish a multi-linguistic prototype of the constructions. To that end, data from several giga-token corpora of contemporary spoken English and Spanish (parallel and comparable) have been selected. This study advances the explanatory potential of constructional idioms for the study of idiomaticity, variability and cross-language analysis. In addition, relevant findings on the dialectal distribution of certain idiom features across both languages and their national varieties are also reported.