" Disable arrow keys in normal mode
" (NOP stands for No OPeration.)
no <Up> <Nop>
no <Down> <Nop>
no <Left> <Nop>
no <Right> <Nop>

" Disable arrow keys in Insert mode
ino <Up> <Nop>
ino <Down> <Nop>
ino <Left> <Nop>
ino <Right> <Nop>