"I can't write that for tomorrow, my do-homework-finger is broken"
"I'm sorry, I got both my arms amputated, I can't."
"I can't, I just can't! I just lost both my legs!!"
"Sorry, I can hear you, I am wearing fake ears, I had my real ones removed."
"Sorry, I have to take my medicine"
"I can't come, I just received news that... That I'm not going to come."

It's even better if you do popping sounds with your mouth while explaining. "My arms... They just fell off!!! It was like *Pop* *Pop*"
"I'm sorry, I got both my arms amputated, I can't."
"I can't, I just can't! I just lost both my legs!!"
"Sorry, I can hear you, I am wearing fake ears, I had my real ones removed."
"Sorry, I have to take my medicine"
"I can't come, I just received news that... That I'm not going to come."
It's even better if you do popping sounds with your mouth while explaining. "My arms... They just fell off!!! It was like *Pop* *Pop*"