Please just refrain from saying things behind people's back that you wouldn't say to their face.

Some guy this morning started shit talking me as soon as I walked away and he thought I couldn't hear. Made for a bad morning.

Unless you have a good reason—like you fear for your safety or someone might interpret your words the wrong way—don't say things behind people's back that you wouldn't say to their face. Especially seconds after they walk away. That's called being two-faced and cowardly.