I guess that's it
The fake agreement people use when they're too lazy to actually say yes or no and just want the conversation to die.
'I guess that's it' when asked if he wanted more pizza.
'I guess that's it' after being asked if he wanted to go to the movies and he just wanted to go home.
'I guess that's it' when someone asked him if he liked his new haircut and he was too tired to lie.