“All right, I'll let it slide this time.”
You get on the bus, but you don't have complete fare. You tell the bus driver you're very sorry, but you're late for school. The bus driver says that you can ride anyway.
All right, I'll let it slide this time.
This is a casual phrase that means "OK". Use it to agree with what someone has said:
All right, sure. Let's give it a try.
All right, I'll be there at 9:00.
We use "let ___ slide" when someone breaks a rule, but it’s not too serious. An authority figure might “let it slide” by ignoring the incident, or not punishing the person who broke the rules.
I let it slide the first time, but twice was too much.
They usually let it slide if you have a good record.