Flunked

Doing spelling with my mr. Carter and we came acrossed the word "flunked". I said to him "say it, spell it and use it in a sentence".
He says "flunked, f l u n k e d" and trn his sentence was as follows. "I think I just flunked in my swim shorts."

What exactly does flunked mean these days.

He later gave me the correct meaning. He is a crack up.