If you start backing up and hear a beeping noise, you're probably overweight.
Combine BMI and fat percentage. If your BMI is too high, but your fat percentage is low, then you're muscular and don't have to worry about it. BMI, in and of itself, doesn't tell the whole story.
For males, a body fat percentage of under 20% is accetable, with 10% being excellent. Professional boxers generally try to aim for 5%. Women have a slightly higher acceptable percentage because they usually have two large repositories for fat on their chests (which is a good thing, mind you).