Someone who's no-nonsense is very efficient and businesslike. If you're extremely practical and don't see the point of wasting time, you're no-nonsense.
Some teachers like to joke around with students, while others are much stricter than that — they are stern and no-nonsense. A brand new English teacher might resolve to start using more no-nonsense techniques in the classroom if he realizes his class isn't getting quite enough accomplished. The adjective no-nonsense was first used in 1920s sporting slang, originally in the phrase "to stand to no nonsense."