Etiquette is more than good manors, it is knowing what to do in a social situation.
Con, is the skill of being able to tell a really good lie, fast talking and social engineering.
Intimidate, is the skill of being of appearing threatening. I would also add torture to this skill.
Negotiation, is the skill of bartering, it may be for pay or paying less for that new car. It does not matter if you are pornomancer with this skill maxed out people have limits they are willing to pay for things. (No, you can not buy an assault cannon for ¥50, and I am not paying you ¥1,000,000 to walk my dog)
These are skills that PCs use, and NPCs rarely ever use if ever in actual play. Do you think if if part of the run the GM is planning for the Mr.J to double cross you that the Mr.J is going to roll a con skill. I kind of doubt it. Or that a key plot will never unfold because the a PC was able to resisted an intimidate roll.
I think a composure skill is kind of lame and would be a waste of BP or karma. If you need a skill to counter a skill, I would use ether the same social skill or another social skill if appropriate to counter.