can go many ways, used in different instances, as "quit being a little bitch", or "do it, you pussy." and can also be used in place of "fuck you/off", or finally just to call someone afraid of something.
MAN1-"i don't want to go to work tommorrow."
MAN2-"boss up,lazy ass"
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"i guess we're just gonna have to boss up and go."
Take ownership of ones life, by directing the full capacity of their time, resources, and attention toward a specific direction, goal, or intent. In other words: step up, raise your standard, up your game, and take responsibility for the direction of your life and the full maturity of your dreams.
Stop putting off your dreams until tomorrow ... boss-up and make it happen today.
And dying in yo' bed many years from now, would ya be willing ta trade all da days from dis here day ta dat fo' one chance, just one chance, ta come back here as young men an' tell our enemies dat dey may take our lives but dey will never take our freedom ... YUB NUB!