No can do
Definition 1 of 1
Pro Tip 1/3Slang Usage
Used informally, often among friends or in casual conversations. 
Can you finish this project by tomorrow? No can do, that's unrealistic.
Pro Tip 2/3Polite Refusal
A light-hearted or humorous way to say you can't do something without sounding rude. 
Could you cover my shift this weekend? Sorry, no can do! I have plans.
Pro Tip 3/3Not Formal
Avoid using it in formal situations. Use 'I can't' or 'I cannot' instead. 
In a job interview, instead of saying 'no can do,' say 'I am unable to do that'.