think nothing of it

think nothing of (someone or something)

To have little or no regard or concern for someone or something. Your boss seems to think nothing of you, judging by the way she speaks about you behind your back. These corporations think nothing of the rights and desires that the consumer might have—all that matters to them is the bottom line.
See also: nothing, of, think

think nothing of it

Don't worry about it; no need to thank me or apologize; it isn't a concern or inconvenience for me. A: "Thank you so much for looking after the kids while I was in the hospital—I don't know what I would have done without you!" B: "Think nothing of it, I was more than happy to help." A: "I'm sorry if I got you in trouble with the boss." B: "Oh, think nothing of it, you were just doing your job."
See also: nothing, of, think
Farlex Dictionary of Idioms.

Think nothing of it.

 and Don't give it another thought.; Don't give it a (second) thought. 
1. You're welcome.; It was nothing.; I was glad to do it. Mary: Thank you so much for driving me home. John: Think nothing of it. Sue: It was very kind of you to bring the kids back all the way out here. Alice: Think nothing of it. I was delighted to do it.
2. You did no harm at all. (A very polite way of reassuring someone that an action has not harmed or hurt the speaker.) Sue: Oh, sorry. I didn't mean to bump you! Bob: Think nothing of it. Jane: Ihope I didn't hurt your feelings when I said you were too loud. Bill: Don't give it a second thought. I was too loud.
See also: nothing, of, think
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.

think nothing of it

do not apologize or feel bound to show gratitude (used as a polite response).
See also: nothing, of, think
Farlex Partner Idioms Dictionary

think nothing ˈof it

(spoken, formal) said as a polite reply when somebody has thanked you or said sorry for something: ‘I’m terribly sorry for all the trouble I’ve caused you.’ ‘Think nothing of it.’
See also: nothing, of, think
Farlex Partner Idioms Dictionary

think nothing of it

You’re welcome; it’s no big deal. This airy dismissal of thanks came into wide use around 1940 on both sides of the Atlantic. It survives, though it is rapidly being replaced by no problem. An early appearance in print was in Terence Rattigan’s play The Sleeping Prince (1948), in which Mary responds to “I shall not soon forget your kindness” with “Think nothing of it.”
See also: nothing, of, think
The Dictionary of Clichés by Christine Ammer
See also:
  • think nothing of (someone or something)
  • think little of
  • think little of (someone or something)
  • judging by
  • judging by (something)
  • judging from (something)
  • the pot calling the kettle black
  • mouthpiece
  • pot is calling the kettle black
  • the pot is calling the kettle black