Every time you paste code on your buffer from your clipboard (if you use vim on a terminal) it will auto indent or auto comment in a top to bottom way your lines of pasted code.
If you want to avoid this behavior you simply have to switch to paste mod via:
of course it's easier to map it on the keyboard like this:
nnoremap <F2> :set invpaste paste?<CR> set pastetoggle=<F2>
Now F2 will set your insert mode on.
Hope it helps!