To simplify the expression \( (x+1)^2 - 9(x+1)^2 - 9 \), we can start by combining the like terms.

First, notice that \( (x + 1)^2 \) can be treated as a single term. Let's set \( y = (x + 1)^2 \). Then the expression becomes:

\[
y - 9y - 9
\]

Now, combine the like terms:

\[
y - 9y = -8y
\]

So we have:

\[
-8y - 9
\]

Now, substitute back \( y = (x + 1)^2 \):

\[
-8(x + 1)^2 - 9
\]

This is our simplified expression. If desired, we can expand it further:

1. First expand \( (x + 1)^2 \):
\[
(x + 1)^2 = x^2 + 2x + 1
\]

2. Now substitute it back:
\[
-8(x^2 + 2x + 1) - 9
\]

3. Distributing \(-8\):
\[
-8x^2 - 16x - 8 - 9
\]

4. Combine the constant terms \(-8\) and \(-9\):
\[
-8x^2 - 16x - 17
\]

So, the fully expanded form of the expression is:

\[
\boxed{-8x^2 - 16x - 17}
\]