请帮忙看下这句英语of all the days for this to happen

请帮忙看下这句英语of all the days for this to happen
今天看了个英语短篇,说得是一个小孩,上学老迟到 .一天,他气得特别早,一早就出发,以为自己今天肯定不会迟到.可路上他的滑板撞上了块石头,他晕了过去.当他醒来时,feeling groggy and confused.就往教室赶,oh,no,he thought,as he climbed up the stairs of his school.Of all the days for this to happen!
Of all the days for this to happen是什么意思呢?