As soon as you get a new pair of underwear home and unwrapped, it's important to try it on. That means testing out how it handles FES (Full Erectile Stretch). That's a real term I just made up but it's still real.
Look for the "FES-Certified" label when shopping for underwear so you don't end up with loose hanging fabric making unsightly lines and bringing discomfort under your pants. If you even ever wear pants.
It's incredible to imagine, but this pair will bounce back to full seamless tightness even after the brutal treatment by this massive erection. He may have a feature as an underwear tester. If a pair can survive him, they can survive anybody. Of course, a bulge busting out a hole in a pair of underwear is not a tragedy as long as the right guy is nearby to deal with the situation.