(noun) A type of erection where the penis stands erect, but remains soft. A portmanteau of boner and nerf.
Jane: So I finally slept with Bill last night.
Jill: Oh! How was he?
Jane: He was ok i guess. I thought he was hard for me but it turned out to be a bonerf.
Jill: Damn girl!
(noun) When you are so excited about playing with nerf guns, you get a hard-on.
James: Hey dude, get over here right now, i just got me two vulcan 25's and a double shot nerf gun. Let's do some drive-by's
Nic: Dude! You just gave a massive bonerf! I'll be there in 5