Select a victim who is eating something runny e.g. custard, milk, rice pudding.
Just after he has filled his mouth with food, run past screaming "ANGRY DRAGON!" and slap him round the back of the head.
This will hopefully result in the food coming out of his nose - and when he turns to look at you, he will indeed look just like an angry dragon.
If the food doesn't come out of his nose, you still have the chances that he might reflex-swallow and choke on it, or bite his spoon really hard. He'll still be angry, so it's all good.