He relied on his superficial charm to win people over.
empty words
Frequency:
50
%
His promises were just empty words.
shallow gestures
Frequency:
45
%
Her gestures seemed shallow and insincere.
Idiomatic Expressions for plastic person
Phrase: plastic smile
Meaning: a forced or insincere smile that does not reflect true emotions
Usage: He greeted us with a plastic smile, but I could tell he was upset.