My guess is based on what you've posted you will get a warning letter and as long as it does not continue that will be the end of it. There are a lot of variables here though that makes it difficult to gauge a solid estimation of what you will face at the meeting. The big one in my mind being what the 2 witnesses had to say when asked about the incident. If they claim you did make physical contact with each other you might be in hot water. The same goes if they claim they felt threatened by your behavior. Even if they were not the target of abusive conduct, if they felt being around it created a "hostile work environment" UPS and the individual management in your operation can face serious liability problems if they were to fail to react decisively in such an instance.
If you know the 2 witnesses well enough to know how they are going to portray events, you are likely going to be ok. And as 22.34life already said, absolutely make sure you have a representative with you. Management will likely already have plans to have a steward there if they are planning on giving you a warning letter and certainly if it is a termination but, again, from what you've written here I think that unlikely.