Cotton t-shirts are a basic clothing item that everyone possesses. To date, no studies have taken into account the consumers’ perspective, even though they can play an important role regarding the actual environmental impact of their clothing items. Therefore, a life cycle assessment study was performed in order to inform the public about the environmental impacts of a typical cotton t-shirt and the relevance of consumer behavior (i.e., washing and drying) on the overall impacts along the entire life cycle of such a t-shirt. The aim was to provide hints, allowing users to reduce the impacts of their t-shirts. While the production phase was based on global data, the use phase focused on Switzerland as the study was established in the context of an exhibition in the Textile Museum in St. Gallen (Switzerland). With this study, it was found that users have various choices in order to make their t-shirt more sustainable. Wearing the t-shirt throughout its entire life expectancy was found to be the most important factor influencing the overall environmental performance of such a clothing item. The relevance of filling the washing machine to maximum capacity, washing at a lower temperature, or using a tumbler was also illustrated. In addition, choosing materials other than cotton or choosing textiles labelled for lower environmental impacts during production could further improve the environmental performance of t-shirts.