Shellscript - both sh and csh. It has horribly inconsistent syntax, a myriad of ridiculous quoting rules that always explode on you whenever something unexpected shows up as data, almost zero data structures, and you have to fork a process to do anything. If not for the fact that it comes standard on every UNIX system, everybody would be laughing at anyone who tried to write anything serious in it.
I learned to avoid bash really fast: the first script I wrote in it took more then half an hour to get right because I wasn't expecting it to treat 0 as true and 1 as false in the if statement.
