Can a Christian be a vegetarian or choose not to eat pork?

Usually, this kind of people does not have this kind of tradition

Sure, you are free, you can choose. it is not a matter of right or wrong.

Apostle Paul said, "To the weak I became weak, to win the weak. I have become all things to all people so that by all possible means I might save some. " He has freedom in God, but with the freedom he is willing to humble himself, to save more souls. So compared with the behaviors, what to do, what not to do, the motivation is more important, live with God’s love is more important.

What if they are hungry?

Of course, why not

Both is okay. Because the bible doesn’t say that christians do not eat this or that.

1 Timothy 4:4 For everything God created is good, and nothing is to be rejected if it is received with thanksgiving
Matthew 15:11 What goes into someone’s mouth does not defile them, but what comes out of their mouth, that is what defiles them.

What do you mean?
Support or not? Just quoting is not very good.

The answer is: all food are clean for Christians. Supporting scripture:

Mark 7:18-19 New American Standard Bible (NASB)
18 And He *said to them, “Are you so lacking in understanding also? Do you not understand that whatever goes into the man from outside cannot defile him, 19 because it does not go into his heart, but into his stomach, and is eliminated?” (Thus He declared all foods clean.)

Sure. The bible doesn’t say that christians eat pork or not. It’s up to us.