Specifically, in Western Europe. I've heard that they could be if they broke their code, and that the ceremony after they were kicked out was quite elaborate, including a funeral in which they were put in a casket. Can anyone verify this? And if so, can you provide some sources that discuss this?
Well, the main reason why funerals happened was because ex-knights were really dead. They weren't just symbolic, to take away a knight's coat of arms and privileges often were tied to death penalty, like betrayal or cowardice. Few people were degraded and survived, I have Maurice Keen's Chivalry at hand, and it shows some interesting examples of ceremonies.
Sir Rudolf Grey, who commanded Bamburgh castle in the War of Roses, and lost to Edward IV was judged as guilty of treason. His knightly spurs (symbolic of a cavalier) were ^edit cut off by the cook's (low servant's) cleaver, and he had to wear his own crest reversed as he was going to the execution. However, his descendants were not degraded, as Grey's grandfather was loyal to the Yorks.
On the other hand, Andrew Harclay was in 1323 convicted of spying for Scotland - his tunic was torn to shreds, his spurs were taken away, and his sword was broken, and his coat-of-arm erased. He was torn by horses and hanged.
Another knight, Peter of Hagenbach was slapped by a commoner before his death, to represent the massive disdain whole mankind had for him.