THEME:   the sound of a phrase when a -TH ending is added changes the meaning of the original phrase   
GOOD ONES:     couldn't find any    but I found 4 Z's   
BTW:   The title "Th-, Th-, That's All Folks" suggests the stuttering of Porky Pig, yet the theme answers are simply phrases to which a "TH" is appended meaning that it's the digraph TH which is germain.  Thus, Chairman Mao becomes CHAIRMAN MOUTH, which would have been good if the clue "Unflattering nickname for a boastful corporate bigwig?" were less wordy.  "Loud boss?" would work.      
Guffaw   YUK [a "guffaw" is loud; a YUK is often a disparaging term for, or a false, laugh or titter]      
More experienced   WISER [would that were so --- wisdom is not reserved for the elderly, so many of whom are unwise]      
Ashton's partner   MYLA [I assume these are stars (I know Aston Kutcher), and if they are lovers why do we not call them so: 
partners sounds like a business arrangement.  Even worse is "sleeping with" as a euphemism for "having sexual relations with" or the Anglo-Saxon term which I much prefer, but which vestiges of our Victorian heritage forbid in "polite" company.]      
Spanish "these"  
 ESTOS [exactly]      
RATING:     

Three grins = Loved it; Two grins = Enjoyed it; One grin = A bit bland for my taste; One teardrop = Not much fun