From a jungler, PLEASE, FOR THE LOVE OF GOD, if you want one of my buffs, ASK before you take it, and if you come to help me take a buff, DO NOT take it. I'm very generous with my buffs and if I don't absolutely need them, I'll gladly give them out. But if you take them without asking or steal them while I'm taking them, forget you. Taking one buff at the wrong time can screw over some junglers really hard.
Example: I was trying to jungle Fiddlesticks today and an Olaf top asked me, "Can I have blue?" for the first blue. I said, "I'll give you 2nd blue, I need the first one pretty badly." He then leashes for me, but throws an axe in at the last second, says "thanks" and runs back to his lane with my buff. I was screwed over for the entire rest of the game because I lost so much jungle time due to being out of mana, and we ended up losing because I couldn't do anything.