Is it bad to become friendly with teachers?

It's not bad at all. If you're being hared about it, it's because other people are jealous, even if they don't entirely understand why. But you need to worry about what -you're- doing, not what other people think you're doing. Always do what you think is best and most correct. And remember, nice guys don't always finish last. They don't even -usually- finish last. That's just some stupid rumor some jealous person started spreading a long time ago.