TTDB is an acronym that stands for Things That Don't Belong. In February 2001, KidKero became room-mates with Number-6. In the process of moving in, there were numerous boxes strewn all over the floor. They'd been unpacked, but some of the items weren't put away yet -- they were stacked in piles on the floor next to the boxes. These were, inappropriately, breakable and fragile items like ceramics, dishes, glassware, etc. KidKero called them Things That Don't Belong (on the floor).
Later on, we were joking online about how KidKero would look with juice-can curlers in his hair, like Shirley Temple. We decided that this too was a TTDB. This led to other "improbably or scarily inappropriate situations" like "Netboy in a scat video" (see: poopbypass); "Nutation at the NTouch" (the NTouch is a gay bar for "gay Asians and their admirers" -- see: (to) spill a drink on Nutation); "Number-6 at an International Socialist's meeting"; etc.