If you are in a trusting relationship then tell her/him the truth.
If you are just starting one with a view of a long term relationship, then you can say that you injured your
Dick years ago and have had some surgery+procedures to fix it and even out the appearance.
If you just wanna bang away, one night stands, say whatever outrageous thing you want like it\'s a freak of nature
Remember, Too many lies eventually catches up with you sooner or later.