Don't need lube, but lube does make it better. Though I wouldn't use somebody elses conditioner that's just plain rude. Neither would I do it in the shower.
VERY FUNNY STORY My very close freind once was masturbating in the shower, and used NOT the conditioner BUT some acne cream or some shit and rubbed it all in....Apparently he had to go to the doctor because layers were peeling off.... LMAO