According to the definition at Merriam-webster dictionary, show up has some negative meaning like followings ;

1) to expose or discredit especially by revealing a faults <showed them up as a frauds>

2) to embarrass or cause to look bad especially by comparison <trying to show up the boss.

However, it has also positive or nutural meaning like these ;

1) be clearly visible, as in “This print doesn’t show up clearly against this dark background”.

2) put in an apparance, arrive, as in “I wonder if he will show up at all”.

3) show someone up : surpass someone in ability, outdo someone, as is “John’s high score on that math test really showed up the rest of the class”.

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