Using multi-modal Conversation Analysis, this article demonstrates how teenage boys end assessments of social experiences with insults. When they participate in social activities, teenagers — as everybody else — routinely make assessments through which they produce social organization and create alignments. This article, however, analyzes structures of assessments that are contested in a counter-positional action. It will be demonstrated how the teenage boys end these challenged-assessment sequences through ‘insults’. A feature of these insults is that the conversationalists ‘go mental’, that (...) is, they question the ‘mental’ abilities and competences of their co-participant and thereby exclude him from the status of being a competent member of the group. In and through such conduct, the participants make the social function as well as the risks of assessing explicit: as competent members of a social group they are being held accountable for having claimed knowledge of the assessed target and may on these grounds be excommunicated as someone who does not understand social life. (shrink)