Green’s Dictionary of Slang

tubular adj.

[? surfer jargon tube, the inside curve of a good wave]

(US teen) the ultimate in perfection.

[US]Frank Zappa ‘Valley Girl’ [lyrics] It’s so AWESOME / It’s like TUBULAR, y’know.
[US]D. Hecht Skull Session 144: Oh, my God. Dudical went out with tubular, God you might as well say gnarly!
(con. 1980s) i80s.com [Internet] tubular Something that is cool. Something overwhelming. ‘Tubular, totally tubular.’.