Her takeoff of the teacher was so funny that the whole class burst into laughter.

takeoff 是名词，由动词短语 take off（"起飞；模仿"）转化而来。这里指"模仿、戏仿"的意思，特指对某人言行举止的夸张模仿。takeoff of the teacher 就是指"模仿老师的样子"。