Real Dictionary

offhand
If you say something offhand, you say it without checking the details or facts of it.
If you say that someone is being offhand, you are critical of them for being unfriendly or impolite, and not showing any interest in what other people are doing or saying.

offhand in American English
said or done offhand; extemporaneous; unpremeditated
without prior preparation or study; at once; extemporaneously
adjective: informal, casual, curt, or brusque
adverb: cavalierly, curtly, or brusquely

offhand in British English
without care, thought, or consideration; sometimes, brusque or ungracious