You want to be received without judgment. Furthermore, you don’t want to be brushed off, yelled at, written off, talked over, underestimated, laughed at, and so on.
Boundaries are most effective when we feel comfortable with the container (a.k.a. limits) we are creating for ourselves. Oftentimes, boundaries help us honor the answer to the question “What do I need?”.
I've learned that when I take the time to identify what I need and share it with my spouse, for example, our presence and connection are enhanced.
When (not if) your teen presents an undesirable behavior or seems "shut down", you have an opportunity to ASK about it, rather than telling them about (aka lecturing them).