Cool_guy129i is an account that Albert very briefly used in the video, This really weird roblox group told me bad things.
Albert wanted to make an account to use in the game Group Recruiting Plaza 4.0. Albert wanted to originally name cool_guy cool_guy128 but the name was already taken so Albert changed the name to cool_guy129, which was also taken. In frustration, Albert hit his keyboard several times which made an i by typed in the username, Albert goes with it and makes the account.
Albert has cool_guy join Group Recruiting Plaza 4.0 only for him to be immediately disconnected due to cool_guy being less than 30 days old. Albert digs up an old account named Yyc4352 and contemplates whether to wait 30 days and use cool_guy or use yyc. Albert ends up doing the latter, abandoning cool_guy by doing so.