Is there a word for overly friendly speech from someone who insults you behind your back?

Is there a verb or adverb to describe the overly friendly speech or tone of someone who has said something bad about you behind your back but doesn't know that you know?

Solution 1:

Hypocrite, meaning he who speaks with forked tongue, or perhaps 'two-faced' is a better fit, although I have to say several other choice expressions do spring to mind, not least being slimeball. Or perhaps more kindly, coward.

Solution 2:

you can also use the words phony-baloney or mealymouthed

Solution 3:

You may be best served by a nice descriptive adjective in this case. Here are a couple that fit:

saccharine

adjective

too sweet or sentimental : sweet or sentimental in a way that does not seem sincere or genuine
_{Source: Definition of “saccharine” at merriam-webster.com}

cloying

adjective

1. causing or tending to cause disgust or aversion through excess:
   a perfume of cloying sweetness.

2. overly ingratiating or sentimental.

_{Source: Definition of “cloying” at dictionary.com}

Either can be made into adverbs in the usual way (by adding “-ly”), the latter more comfortably than the former (though “cloyingly” should probably always have “sweet” tacked onto it in use).