To my astonishment, I've just read this statement about the expression "Thanks a lot" in my Longman dictionary:
We usually say " Thanks a lot " in everyday language, and so is it improper to say it?thanks a lot
also thanks a bunch American English spoken used when really you are annoyed about something and you do not mean 'thank you' at all
May you please give us the gist of the above-mentioned quotation?
--- Thank you ---