Try and help even though neather of you will make it.
Run away so you don't fall also
Do what ever it takes to make sure the person that is falling is safe
Ignore them "It's not my problem."
Find out whats wrong
Find out what wrong and comfort them
Find out what wrong and fix the problem
Invite them to sit with you.
If they try and sit with you tell that someone is going to sit there.
If they sit with you, you move to a different spot hoping they won't follow you.
Invite them to sit with you and intorduce them to the other people sitting at the table.
Don't answer it.
Answer and tell them you cant talk at the moment.
Talk to them anyway.
Tell them you don't want to talk to them.
Have someone tell them you hate them.
Talk to them and find the problem.
Tell them you are mad at them and why.
DON'T TALK TO THEM ANYMORE.