Top bad practices in PHP

Programmer Question

Hi

Until now I've learned from Stack Overflow that some of the code I've been writing so far is considered "bad practice". Like using tons of global variables, create_function() etc. I'm curious to know more about this.

So please post here what you think are bad practices in PHP and why. But please only one per answer, this way the worst can get the most votes.

thanks :D

Find the answer here