Someone who is 'straightish' is someone that is straight as far as the normal beholder, but has sex with the same gender behind closed doors on a regular basis. One can seem (and be therefore deemed) straightish, or it may have been proven.
"His outfit is perfect! Is he gay?"
"I mean... he's straightish."

or...

"I'd love to suck him."
"He's straight.."
"Ehh... ish."
by Jordan_B February 25, 2010
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Someone who acts really gay but is actually straight.
"Are you gay?"
"No, I'm straight... ish"
"Your straightish?"
"Yep"
by Katieblablabla June 26, 2017
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