Let's simplify the given expression step by step:

Distribute the 4b to both terms inside the parentheses:
4b(5a) - 4b(b) - (5a-2)(5a+2)

Simplify the expression:
20ab - 4b^2 - (25a^2 - 10a + 25a - 4)

Combine like terms inside the second set of parentheses:
20ab - 4b^2 - (25a^2 + 15a - 4)

Distribute the negative sign to all terms inside the parentheses:
20ab - 4b^2 - 25a^2 - 15a + 4

Therefore, the simplified expression is:
25a^2 - 15a - 4b^2 + 20ab