that's about the size of it

act one's age, not one's shoe size

Synonym of act one's age (“to behave in a mature manner; to avoid being childish”).

cut down to size

To humble or humiliate, especially someone or something that is perceived as overly domineering or too proud.

pick on someone your own size

An admonition of cowardice, usually said to make someone cease harassing or bullying someone else, especially where the bullied party is physically smaller or weaker than the bully.

size queen

One who prefers sexual partners with large penises.

size up

To evaluate; to estimate or anticipate the magnitude, difficulty, or strength of something.

that's all she wrote

Indicating an abrupt termination of a project, or of one’s hopes or plans.

that's done it

Used to announce a successful solution to a problem.

that's just me

Indicates the expression of a personal opinion, but often used ironically as an understatement.