To Screw Up
When you screw-up, you make a big mistake. To “Screw-up” is a slang expression and we use it when something has gone wrong.
E.G. “I thought the exam was today but I screwed up! It was yesterday so I missed it!
A blunder is what happens when you make a silly mistake.
E.G. “I blundered when I thought the woman was a man!””
To Put Your Foot in Your Mouth
When you put your foot in your mouth, it means that you say something that you shouldn’t have said.
E.G. “I told Johnny about the party we have arranged for him, but he didn’t know about it. I really put my foot in my mouth and now he knows about the surprise party!