A term used to hide the fact that you are actually crying due to being moved emotionally by implying that you are crying because someone must be cutting onions.
When Jack saw the video of the lost dog being reunited with its owner he began to tear up and exclaimed, "Who's cutting onions!"
its a term used to put your arm around someone. you start with counting ur far shoulder away from them as one, two which is the closest one to them, 3 their first and 4th the farthest one on the other side and keep ur arm around them
Assuming you will have something before you actually have it; similar to "counting your chickens before they hatch" (which is commonly attributed to Aesop).