Green’s Dictionary of Slang

reamer n.

1. (US Und.) a cheat, a swindler [ream v. (1)].

[US]Ersine Und. and Prison Sl.

2. in sexual senses [SE ream, to enlarge a hole ream (out) under ream v.].

(a) (also reemer) a sodomite.

[US]Irwin Amer. Tramp and Und. Sl. 94: Gut Reamer.–A vulgarism best undefined.
[US]Monteleone Criminal Sl. (rev. edn).
[US]Eble Campus Sl. Mar. 5: reemer – homosexual. Derog. Used as an insult to non-homosexuals: Finish the workout, you reemer.
[UK]R. Milward Man-Eating Typewriter 234: ‘Les indédirables’: rent-boys, weirdies, roamers and reamers [...] suburban losties.

(b) the penis.

[US]Monteleone Criminal Sl. (rev. edn).