Too Dumb; Can't Think. An appropriate response to "TL;DR," a.k.a. "Too Long; Didn't Read." Can also be used as TD:DT (Too Dumb; Didn't Think), TS:CT (Too Stupid; Can't Think), and TS:DT (Too Stupid; Didn't Think.) Could also be followed with either smh (Shaking My Head) or stfu (Shut The Fuck Up) - both are implied.