It sounds like you encountered a challenging situation that left you feeling uncomfortable and unsure about how to address it effectively. Here are some suggestions on how to communicate your feelings to your boyfriend regarding his behavior with his niece:

1. Choose the Right Time and Place

Timing and environment matter when discussing sensitive topics. Find a calm and private moment when both of you are relaxed and not distracted. This can help create a more open atmosphere for dialogue.

2. Use "I" Statements

When expressing your feelings, it's beneficial to use "I" statements to communicate your perspective without sounding accusatory. For example:

• Instead of saying: "You were being weird with your niece."
• Try saying: "I felt uncomfortable when you touched your niece's hair because it seemed like she didn’t want that."

3. Explain Your Concerns

Clarify why you found his behavior inappropriate. You might say:

"I understand that you may not see her in a way that makes you think it's inappropriate, but she is a teenager, and physical touch can be misinterpreted. It made me uncomfortable because it felt out of character for you and seemed to make her uncomfortable too."

4. Emphasize the Importance of Boundaries

Discuss the importance of respecting personal boundaries, especially with younger individuals. You could mention:

"It's important to respect people's personal space, especially since she is a teenager. Many young people are sensitive about their bodies and may not feel comfortable expressing discomfort directly."

5. Address His Response

If he shrugs off your concerns, remind him that your feelings are valid. You might say:

"I understand you might think it's harmless, but I hope you can appreciate my perspective. I want to ensure we both respect each other's feelings in our relationship."

6. Offer Alternatives

Suggest more appropriate ways for him to interact with his niece that don’t involve physical touch. For example:

"Maybe you could engage with her through conversation or joking around instead of touching her hair. That way, you can still have fun without making her uncomfortable."

7. Be Prepared for a Dialogue

Encourage an open discussion where he can express his feelings and thoughts. Listen actively and be ready to engage in a constructive conversation.

8. Reiterate Your Feelings

Finally, remind him that your intention is to ensure both his and your feelings are respected. You could close with:

"I care about you and your relationship with your family, but I also want to make sure we communicate openly about things that make us uncomfortable."

By approaching the conversation with empathy and clarity, you can foster a better understanding between you and your boyfriend. It's important to establish boundaries that make both of you feel comfortable and respected in your relationship.