Tell the WHOLE truth

This rant is not because I'm lazy, it's about the difference between telling someone the whole truth, and only telling them part of it.

As previously mentioned on here, I bring a company car home on Monday nights, as I have to work outside of the school on Tuesday mornings and afternoons. Yesterday, I took the key to the black car at about 17h, as I always do. Shortly after that, Incompetent Colleague came over and asked me for it. I hesitated, but then he said he was just going to have it washed and put petrol in it, implying (by using the word 'just' and his tone of voice) that it'd be back before I left school for the evening. I gave him the key, and he ran out the door.

I walked into the office and Bossman asked me if I had a key to a car, to which I replied that I had just given it to IC. BM took the other key and told me I'd have to come to the school in the morning to get a car, because he needed one (he was too lazy to walk home again....he lives closer to the school than I do) and that IC needed one for the evening. I told him that IC had implied that he would bring one back before I left, and BM told me that he was keeping it overnight and had asked him if that would be okay (to which BM agreed).

Had he said, 'I'm going to put petrol in it, wash it and then need to use it this evening. I'll have it back for you by 8h30 tomorrow morning,' this post wouldn't exist.