It implies that some people are two-faced -- that they will talk negatively about you, but will not say the same things TO you.
:Pope Pius 1 because he know his cards were dissing him out of jealousy.
It means they are hypocrites
It means that most people will easily talk behind a person's back when they are not present. If this person is physically present, these people turn into complete cowards and will be all PLEASE and THANK YOU, while all the while they want to stab this person's eyes out. It reminds me of what Killary Clinton's entire life must be like. Everyone HATES her...but when she is in their presence...all "hail the queen".
It means, when you face someone who talks or gossips about you behind your back, they will be all friendly and nice and pretend they like you.
Sometimes they are just rude and insult you to your face.
It means ur gay