grandstander vs show-off

grandstander and show-off both are nouns.

Word	Noun	Adjective	Verb	Adverb
grandstander	Yes	No	No	No
show-off	Yes	No	No	No

As nouns, show-off is a hypernym of grandstander; that is, show-off is a word with a broader meaning than grandstander:

grandstander: someone who performs with an eye to the applause from spectators in the grandstand
show-off: someone who deliberately behaves in such a way as to attract attention

Other hypernyms of grandstander include exhibitionist.

grandstander (noun)	show-off (noun)
someone who performs with an eye to the applause from spectators in the grandstand	someone who deliberately behaves in such a way as to attract attention