The concept of boredom has recently attracted the attention of researchers in L2 education. As most of the available literature has focused on traditional, in-person classes, very little is known about how L2 students experience this aversive emotion in online classes, especially those prompted by the COVID-19 pandemic. To fill this gap, this large-scale, qualitative study surveys the opinion of 240 demographically versatile English major students from twenty-five universities in Iran to identify the activity types that are more likely to induce boredom in online classes. Thematic analysis of data, collected through open-ended questionnaires and semi-structured interviews and analysed through MAXQDA software, revealed ten different activity types which were boredom-inducing due to their non-engaging or cognitively (un)demanding nature. The findings are then discussed in light of relevant theories of boredom, and suggestions are given for making these activities less boring in online classes.