Said if they call you a square, don’t get bent out of shape

from XV – Be There, Be Square Lyrics on Rap Genius

Meaning

A square is usually a person who is regarded as dull, noticeably un-hip, or lame but if someone were to call you that, don’t let it bug you (or don’t get bent out of shape as XV cleverly stated as a play on with shapes) because that’s who you are and nobody can take that from you.

Also a reference (and shout-out) to all the Squarians who are, as XV put it:

Young, energetic, creative, imaginative individuals who believe in being themselves, different from society and aren’t conformists

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