Green’s Dictionary of Slang

swingy adj.

[swing v. (9); swing both ways under swing v.]
(US gay)

1. bisexual.

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[US]B. Rodgers Queens’ Vernacular 192: swingy 1. bisexual.

2. enjoyable.

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[US]B. Rodgers Queens’ Vernacular 192: swingy [...] 2. fun; predecessor of groovy and kicky.