Would you suggest to use duct tape to hide my gynecomastia?

Ouch!: Duct tape is not designed for skin. I would think that it would be painful to remove. Try some medical grade tape - kinder & gentler, if you must tape. Of course, surgery is really the ultimate answer for this problem.

Ouch!!!: Man i gotta tell you... That does not sound pleasant! find yourself a good plastic surgeon nearby and get them fixed! duct tape is up there with the "bro" and the "mansier" from seinfeld!

Tough on Skin!: The adhesive on duct tape is a bit rough on the skin. Medical grade tape is a better choice. If the problem is confined to the nipple/areola, minor surgery can remove the extra stuffing and smooth things out permanently both in and out of clothing. Consider consulting with an experienced board certified plastic surgeon in your area for more information.