It's a combination of the phrases "come on/c'mon" and "oh my gosh".
You're behind a car and the light turns green, they don't go..."C'mosh just go already!

You're waiting to fuck your trick that you picked up at the bar and he's taking forever douching in the bathroom..."C'mosh! I'm losing my boner."

Come on C'mon Oh my gosh
by Chuckdoody August 5, 2017
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