"Are you sure you're ready to marry him?"
Traditionally, when you hear a friend has gotten engaged, the first thing you say is "Congratulations!" and then do that group squeal-thing we girls are known for.
It's supposed to be a crazy-exciting moment and, regardless of how you feel about your friend's fiancé, it's a time for celebration, and nothing else. Rejoice and be happy in the engagement unity of two.
Avoid saying the following five things:
1. "I can't believe you said yes. Seriously?"
This implies there was a really good reason for your friend to say no and will cause your friend to ask why you would say that. Although you might just be expressing surprise over the engagement, it's going to sound like you don't think she should have accepted the proposal.
2. "Are you sure you're ready to marry him?"
Every newly engaged woman questions whether she's ready to get married, but it's not a question for her friends to raise when they first find out about the engagement. As a friend, your job is to be excited and encouraging. If she's uncertain, she's going to tell you that on her own soon enough.
3. "I'm invited, right? Can I be a bridesmaid?"
Nobody knows who is invited beyond immediate family, until they've had time to sit down and really crunch the headcount numbers. Every future bride faces the dilemma about which friends and family to include in her wedding party, so putting her on the spot is rude. It's a decision that should be made in a thoughtful way, not spontaneously because somebody was tacky and asked.
4. "Do you like the ring?"
This implies that you do not, in fact, like her ring, and you're wondering if she does. If she doesn't, she'll tell you later. You don't have to ask.
5. "What did his parents say?"
This question sounds like you expect his parents to object to the union. Unless you've previously discussed this specific issue with the new bride, don't open pandora's box.