The sudden boos from the audience visibly discomposed the speaker.

discomposed 是动词 discompose 的过去式。discompose 由前缀 dis-（表示"否定、相反"）和 compose（"组成、使镇定"）组成，字面意思是"使失去镇定"，即"使不安、使慌乱"的意思。