From my time as an SO the worst trip was Auckland, 3 crew upto 1130 flight time through the night, with Cabin crew whom just have not learnt how to close the flight deck door quietly, therefore ensuring no sleep.
I remember one !@#@!!@ austrailian cpt... he would sh@ft the SOs even when it was a day flight for him, i always put it down to the fact he was not as capable as the rest of the cpts at CX and therefore needed everything going for him.
But dont be put off as you fly with guys like that once every 6 months and the have to live with themselves permanently. and as stated theres always the 8-10 days off to recover, now im an FO i have lost my tan and forgot what sand feels like.