Evil Communications Corrupt Good Manners

The thought came to my relief that the gentleman might be what is popularly called a Rapper: one of a sect for (some of) whom I have the highest respect, but whom I don't believe in.
...
"The conferences of the night began," continued the gentleman, turning several leaves of his note-book, "with this message: 'Evil communications corrupt good manners.'"
"Sound," said I, "but, absolutely new?"
"New from spirits," returned the gentleman.
- Charles Dickens, "The Haunted House" (1859)

The above quote is almost entirely unrelated to today's blog post.  Forgive me.

We all know that "bad company corrupts good morals," right?

We also know that Jesus lived his life as an example for us to follow, right?

Then what in the world did Jesus mean by eating and drinking with tax collectors, prostitutes and other public sinners?! 

Does He want us all to lose our morals?  Doesn't He, of all people, realize we're fallen beings with concupiscence, weak in the face of peer pressure and temptation?

Yet Jesus also said, regarding one who gives scandal, "It would be better for him if a millstone were hung round his neck and he were cast into the sea, than that he should cause one of these little ones to sin" (Luke 17:2, also Matthew and Mark).

Something's gotta give.

It seems that Jesus, in dining with public sinners, was only offending (not technically "scandalizing" or leading into sin) the self-righteous scribes and Pharisees.  If only they had loosened up a bit, they could have enjoyed some pretty awesome parties with Jesus.

My question is this: to what degree should we associate with those whose moral standards are lower than ours, and to what degree should we avoid them?  When does it become no longer a case of building a relationship as a foundation for evangelization, and instead become a dangerous association to be avoided?

If you're in the workforce, it is likely that you are required to work with someone who has relatively low moral standards.  Yet for the sake of your work environment, or even just to be able to work together, you have to make some effort to be on friendly terms with your coworker.  So when does friendliness becomes dangerous, either in its likelihood to scandalize others by allowing them to class you with those of lax morals, or in its likelihood to laxen your own morals?

I'm not going to presume to lay out any groundrules for interactions with "immoral people," concerning how familiar we can safely be with them, or how distant we must be.  I think that would be a good topic for discussion.  What I can offer is one very practical suggestion, a very small part of the answer--but hopefully a useful one.

When I talked this problem over with a friend of mine, he unwittingly inspired me with this idea.  If we're going to talk about following Jesus' example in being friendly with sinners, then let's take a practical tip from Jesus, shall we?  Jesus didn't see a problem with eating with public sinners, so maybe we could start by going to lunch with these coworkers.  It's not like you're joining their family or anything, but yet it's a great opportunity for evangelization and just for getting to know them better.  For what better facilitator of conversation, than food and drink?  And what better way to get to know someone, than through conversation?

As for finding a complete answer to my main question on the parameters of friendships with those of different moral standards: let's have some conversation of our own below, shall we?

And when you're at lunch with your atheist coworker, just remember, actions speak louder than words... so mind your manners.  Or do I mean morals?