University of Denver. Let's talk. The Professional Psychology Clinic (PPC) is the training center for the Graduate School of Professional Psychology at the University of Denver. The PPC has provided low cost, high quality psychological services to Denver's community for over 30 years.
upset - thrown into a state of disarray or confusion; troops fleeing in broken ranks; a confused mass of papers on the desk; the small disordered room; with everything so upset
The expression upset the apple cart is very common in the UK. Basically it means overturning the status quo. In some ways Don't upset the apple-cart is a little (I stress a little) like Let sleeping dogs lie.