I once wrote a short fortran program and tried to compile it on some obscure IBM mainframe. I used the variable name "abs". Turns out "abs" was a reserved word, an for that slight oversight I got 27 pages of error messages.

Using the original "make" program on UNIX, if you typed "make love" it would
respond "Don't know how to make love. Stop."

Ahh, the good old days...