Who laughed at you? Given sentence is in simple past tense and it is in active voice. Rule : Subject + (was/were) + V3 + Other agents
From Voice · English Language Competence Test
Have you shut the window?
Big Cars must be driven very carefully.
The box can contain no more.
Will no one tell me what she does?
You must look into this matter.
Where did you send the parcel?
I am doing sums.
A big crowd chased him and later the police arrested him.