Knowing how valuable friendship is, we should be very careful in making friends. A good friend is helpful to us while a bad friend would be harmful.

知道友谊的珍贵，我们就该谨慎交友。好朋友对我们帮助很多，而不好的朋友则贻害无穷。日久见人心。

youdao

I can't believe I forgot your birthday. I am such a bad friend!

我真不敢相信居然忘记了你的生日。我真是个不称职的朋友！

youdao

"My friend was a genuinely good person who just made some bad choices in life,"

VOA: standard.2009.10.21

For example, I can-- and having the past experience-- envy towards my best friend, that in and of itself does not make me a bad person.

举个例子，我可以…,因为以前的经历-,嫉妒我最好的朋友，那种情绪本身不代表我是个坏人。

哈佛公开课 - 幸福课课程节选

"The prime minister is leading Greece through challenging times, but as I told him during our meeting in the Oval Office today, whether in good times or in bad times, the people of Greece will always have a friend and a partner in the United States."

VOA: standard.2010.03.11

You may feel like a bad friend.

FORBES: Nine Practices to Help You Say No

And McLain has a vocal range beyond the chilly bad best friend of Portal.

FORBES: Del Toro's Pacific Rim: I'm Making A Note Here - Huge Homage

Of course, he might have been newly appointed, but his command of the English language was so bad that our friend was immediately suspicious.

FORBES: A Speaker Scam - Update