Our Pastor in church sunday said an insincere and evil friend is more to be feared than a wild beast; what did he mean?

An "insincere and evil friend" is more likely to get closer to you and do more harm than a wild beast... which you'd probably avoid altogether.

This is a sound warning no matter who uttered it.

We know what to expect from beasts.  They are straight-forward and don't operate out of malice, as opposed to humans who pretend to be on our side but aren't.  We don't even see it coming.

He's trying to brainwash you into only having Christian friends. That way he has more control over you.

Because insecurities indicate they might do something to protect themself

He meant to scare you.  So be certain to put a couple of C-notes on the collection plate.

 10:28 

Do not be afraid of those who kill the body but cannot kill the soul.

An evil and insincere friend will bring you down to his low level and cause you to go to hell, better to be killed by a wild beast and go to heaven. 

An insincere friend will stab you in the back while smiling and looking you in the eye, you will know the threat from a beast when you see it.