blurt - to say (something) suddenly and without thinking about how people will react
Although the Merriam-Webster definition doesn't actually mention it, blurt out is a common form.
OP's specific context ("You say XXX") doesn't match any standard English expression. There are various slangy versions of "You talk / You're talking XXX" (where XXX may be rubbish, rot, crap, [bull]shit, bollocks, etc.). But they all focus on the idea that what you're saying is worthless, rather than that you're speaking without thinking.
Possibly "You're talking out of your ass" might come close to "without thinking", since to some extent it's modelled on "You're talking off the top of your head".