the problem with saying 'constantly feel the need to organise everything' can be a negative point for you due to two things:
1) it sounds cliched, like 'i am a perfectionist', so the interviewer might feel that you are lying just to relate it to the job.
2) the interviewer might have 20 other applicatnts whos' worst quality is a constant need to organise everything'. Also, your worst quality reads, to me, like a good thing. therefore, interviewer might feel that you are telling them what they want to hear, and that you are not really being honest.
In my opinion, answering 'what is your worst/least best quality' is an opportunity for you to list a minor misgiving about yourself and then say how'll turn it/have turned it into a strenght, eg, 'because i'm from another country i am quite shy, but in order to overcome that i have participated in my school's (uni's) drama club and have starred in a number of plays. This has benefited me because i now find myself my more confident and outgoing around people.'