It's laging when it's loading. If you would give this game few seconds to load levels and etc, you could play it smoothly.
Angry birds is designed for high class Android devices, not for medium class devices like our Optimus One.
The thing that lags is game physics.
If you want to play it without lag, and score many points in the benchmarks, you can install Megatron ROM. It's has many modifications, that allows Optimus One to go further with perfomance.
LG Optimus One <3