巧言令色少なし仁。

Fair words butter no parsnips.

盗人にも仁義。

There is honor even among thieves.

あいつは口ばかりで、誠意がないね。巧言令色少なし仁とはよくいったもんだ。

They say fine words are no virtue if they're insincere and that's him in a nutshell. He's all talk but doesn't mean a word of it.