In BIGBANG's performance of "Loser" on M Countdown 150514, T.O.P wore a statement jacket that has a detachable neck strap, originally attached to the hood. Its brand is Undercover and the item name is in Japanese, which I cannot read so I'll just copy and paste the item name from the online retailer:
アンダーカバー 総柄モッズコート RED TELEVISION 12
I really like it myself, you can take a look at the jacket details here (sold out) and buy it here.
G-Dragon wore a few band tees for these kinds of performances that I have finds and buylinks for, but I don't bother posting them since they're easily searchable. If you'd still like to see them, please comment letting me know! They're actually quite affordable and I'd be happy to make a post if anyone asks ^_^
* ི•̮͡ુ -ુ ྀෆ⃛* Shelley ི-̮͡ू -ू ྀ
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Image Credits: twitter.com/yiannibb, atwork-plus.net