Mouth

A lying tongue hates its victims, and a flattering mouth works ruin. Proverbs 26:28 ESV

Liars will often try to justify themselves. "I was only trying to protect you!" they might claim if you find them out. But there's no justification for lying.

We might not often think of the recipients of a lie as victims. But that's how Solomon describes them. Evidently the Bible takes deceitfulness more seriously that we often do!

 Flattery isn't bigging someone up, it's setting them up for a fall. If you flatter someone you're being falsely nice to them. So they might feel good about themselves when really you should be rebuking them. 

We might think of flattery as insincere but pretty much harmless. But Solomon describes it as causing ruin. If in a work situation, someone's flattered that they're competent when they're not, it's going to cause problems.

 "Truthful God, may we also be defined by truthfulness rather than lies and flattery. For the glory of Your name, amen"