what you say to someone when they thank you► don't mention it spoken · "Thanks for the lift!" "Oh, don't mention it!"
► that's all right/that's OK informal spoken · "Thank you so much for looking after the children." "That's all right. I enjoyed having them."
► you're welcome especially American, spoken · "Thanks a lot." "You're welcome!"
► my pleasure/not at all formal spoken · "It was very good of you to sing for us at such short notice." "My pleasure!"· "Thanks for dinner" "Not at all - I enjoyed it".
► think nothing of it/it was nothing spoken say this when someone has thanked you a lot for something you have done because they think it was very difficult for you to do: · "You shouldn't have gone to so much trouble, you know!" "Oh, think nothing of it."· "Thank you for all your help. I couldn't have done it without you." "Don't mention it. It was nothing."
► no problem informal spoken say this to show that what someone has thanked you for was really a very easy thing for you to do: · "Thank you for coming all the way out here." "No problem, lady."
► sure American spoken used as a reply to someone who has thanked you for something: · "Thanks for the ride." "Sure, no problem."
the short form of ‘you are’: 
You’re late.