"Oh oops I forgot", " What?? Oh yeah I guess I remember now, what was that detail again?" How to address a colleague that constantly drops balls?
Edited to add: e.g. I told them how to do task X yesterday (and it's a simple one) but it seems to have gone in one ear and out the other - and when reminded of it, I just get "oh yes now you say that it sounds vaguely familiar".... Or in another example, leaving on the dot with a task half finished and when it screws up other's work, saying " yeah I suppose I shouldn't have done that" or such like. I point out the errors in a 'helpful' way but they just bounce off..
They're a "co" worker, not a direct report. If they reported to me I'd have it sorted quickly!!