If you're really pleased about something, you can say, "I'm dead chuffed."

"Chuffed" is an informal word, which means pleased or happy.

For example, Carlo was chuffed to see Maria again; I'm so chuffed that I passed my exam.

Dead is a common way of saying "really" in informal British English.

We usually use "dead" before an adjective, for example, "It's dead hot today."

My best friends are dead cool.

The rain was dead heavy this morning.

So, dead chuffed means very happy.

When was the last time you were dead chuffed?