Don't believe a word he says; he's full of it.

彼の言うことは一言も信じるな。彼はでたらめばかりだ。

When he started talking about his amazing achievements, I knew he was full of it.

彼が驚くべき功績について話し始めたとき、私は彼がでたらめを言っているとわかった。