a- The ring shaped dent or stretched area in your wallet due to a long period of time when your unused condom in your wallet in your back pocket has been sat on repeatedly
b- the red ring at the base of a man's shaft, that goes to the top, due to the idiot using a condom they purchased quite a few years earlier, when they were most likely pre-pubescent, and is much too small, leaving a pressure mark after it's use.
a- "I can tell you have a rubber in your wallet"
"i can see the condom ring from here, haha"
b- "I think my condom's the wrond size"
"why do you think that?"
"Its so small I have a condom ring every time i use it, and sometimes it hurts"
the appearance of a ring (same dimensions of a condom) on the outside of one's wallet caused by a condom being in the wallet for an extensive period of time (i.e. months to years)
Bob: Dude what is that on the outside of your wallet bro?
Dan: Shut up man, you know that is a condom ring...
Bob: It has really been that long since you last got laid?
Dan: Don't act like you've never had a condom ring!
Bob: Nah that ain't me....