quick as a wink: very fast

She racked up the balls quick as a wink.

quicker than you can say Jack Robinson: very fast

Quicker than you can say Jack Robinson, Eddie cleared the table and won the match.

quick on the draw: fast at responding to a situation; the ability to answer quickly.

He’d be a good manager if he were quicker on the draw.

quid pro quo: money exchanged for services. (This expression is usually used to describe corruption and bribery in government).

The governor said that there was no quid pro quo behind the agreement to do business with that company.

quiet as a mouse: very quiet

Their new electric garage door opener is as quiet as a mouse.

quite a few: many

She knows quite a few of the students in the class.

quit while one’s ahead: to be winning and then stop before there’s a chance to lose; quit before losing.

When you’re winning big at a casino, It’s a good idea to quit while you’re ahead.