Green’s Dictionary of Slang

fifty-fifty v.

[SE adv. fifty-fifty, half and half]

(US) to treat in a non-commital manner.

[US]J.T. Farrell ‘Merry Clouters’ in Fellow Countrymen (1937) 398: You got to kiss your mama, treat her right, / Or she won’t be home when you call. / Now if you want my company, / You can’t fifty-fifty me ...