To solve the expression \( \frac{12}{25} - 17 \), we first convert \( 17 \) to a fraction with a denominator of \( 25 \).

1. Convert \( 17 \) to a fraction:
\[
17 = \frac{17 \times 25}{1 \times 25} = \frac{425}{25}
\]

2. Now, rewrite the subtraction:
\[
\frac{12}{25} - \frac{425}{25}
\]

3. Since both fractions have the same denominator, we can subtract the numerators:
\[
\frac{12 - 425}{25} = \frac{-413}{25}
\]

Thus,
\[
\frac{12}{25} - 17 = \frac{-413}{25}
\]

So, the final answer is:
\[
\frac{-413}{25}
\]