I have been "teased" but I wouldn't say bullied. I honestly was a little frazzled but not ashamed. In the end people will respect you if you continue to pray without being ashamed, even the people doing the bullying
The Bible is the word of God and is powerful and helps to give the Christian courage and boldness. Boldness is used in the Bible as a measure of faith. The more faith in God the more bold a Christian acts. Deuteronomy 31:6 "So be strong and courageous! Do not be afraid and do not panic before them. For the Lord your God will personally go ahead of you. He will neither fail you nor abandon you."
I definitely have. At first, I felt a bit embarrassed. But as I kept on doing it, I noticed it made others conscious of their lack of prayer. And pretty soon, whenever I looked up from praying, there were others doing so as well. It actually turned out positively. (1 Peter 2:12)
As long as you don't disrupt anyone you should be able to pray quietly before a meal at school. If you make a huge deal out of it some kids might be bothered.
I wonder though if you concern yourself as well with the bullying of nonbelievers, which is sadly more prevalent since Christians are a majority in the US. A year and a half ago a girl in Rhode Island received death threats and threats of rape from students, teachers, and parents for asking her principal to remove an unconstitutional prayer banner from their gym.
Bottom line- bullying is bad no matter why it is done or who it is done to.