Now that we've settled the dire matter of who is at fault, who is going to travel to Florida to deliver a swift and just KITN to the deserving parties?

I saw almost this exact situation several months back. 1-3 game. Drunk guy in big blind puts out 15.
Three folds. Next guy calls 15. At this point the error was discovered. Dealer tells big blind to pull back 15 and put 3 out. Dealer tells caller to take back 15 and then decide on what to do from there. Floor was never called. No one even questioned the dealers ruling.

If you sense a period of untimely darkness today .. then it was probably your fault. The more dark it is, the more it was your fault. GL

The guy who walked up and distracted the OP to say "Hi" ??

It's probable he didn't realize he was BB, didn't post the BB, and the dealer didn't make sure his BB was out there before dealing him cards, then thought he was UTG since he didn't have a blind out there.

I've seen this happen a number of times, but it's usually the BB attempting to fold.

This sounds very plausible to me. I've almost folded a few times, not realizing I was BB. I can't recall ever trying to raise in that situation.

I've seen cocktail waitresses that made me forget my name every time they walked by let alone the action in front of me. Could be she gets all the blame.

action stands

you can have a mis deal after action has started, for instance supposed someone found two of the same cards in his hand. it is of course a misdeal at most any point in the hand.

what instead here if now someone moved in and the bb said wait a minute the dealer made a mistake none of the bets were legal. you open the door to more problems. so if someone complains it should be a misdeal.

So I can roll over two fours of hearts on the river and say oops it's a misdeal?

It's a voided hand not a misdeal, but semantics aside yes you can. Of course if you do this and the floor thinks you did it purposely and it was heads up the floor may rule you have lost anyway, and may 86 you for cheating as well.

most casinos will rule all money is returned in the hand and its played over with a new deck. totally wrong for someone to get money back at the end as if he knew he ws freerolling on the pot if he made a bluff.

however casinos do it that way. but also what if you looked at your cards and saw two red fours. you may not have studied them to see the suits as you would expect them to be different. so why would you lose on the end. it is a tough call for the floor to make.
and it is their fault for the problem in the first place.

plus in casinos where strangers are playing the deck stub should be counted very frequently. as just spreading it at hands end it can be see quickly the remaining cards.

The BB 's $20 is a raise out of turn. Follow the room's procedure for an out-of-turn bettor.

The first caller's action could be interpreted as a call or a raise to $20, depending on how the chips were put into the pot. Or, it could be considered a gross misunderstanding of the bet he was facing and could be allowed to act de novo. Arguably, it would be unfair to hold him to a raise to $20 if he just slid four red chips into the pot in a manner consist with a raise, since the BB knows his hand is probably capped since he didn't 3bet. It would be less unfair if you had a rule where someone who bets out of turn can't take an aggressive action if the action is backed up and can only call any bet.

What do you do when an idiot who doesn't realize he is the button because it is between him and his neighbor and not directly in front of him, even though he didn't post a blind preflop, decides he is going to lead out on the flop and gets two callers with at least one player still to act when it gets noticed that his action is out of turn?

that why since we are ourselves paying the dealers salaries by tips , we should put more pressure on them and the house to have dealers competent to not make such simple mistakes.

and a good floorman should come to the table and work it out. many times the table is happy with just leaving it as is then do that.

If you act on a fouled hand, then your hand can be declared dead, and you won't be entitled to get your money back on the hand. The other players will get their money back. This is covered in RROP, section 3, irregularities.
This prevents you from bluffing your two fours and then claiming fouled deck only if you get called.

as always your ruling is determined by the whim of the floor person that day. and the firm rules of the house. so learn them. this will almost never come up but ive have seen it a few times where each time i suspected someone switched a card in on a previous hand. that is why it happens.

I saw two red fours. I didn't think to look and make sure they were not the same.

it is the casino's mistake if they deal a fouled deck to the players.

Yup. Significant action. Raise stands.

You can't kill the deal. Two reasons. One, if BB didn't like their cards then they could do this move every time in hopes of getting a new deal. Two, There's been significant action and at that point is too late since the action has also been offered and accepted as Dinesh said.

No because there has been significant action based on BB raise.

generally if there is an illegal bet made it is changed to become a legal bet.

so here with the b blind raising himself i would rule it goes back to the first person to call or raise the blind. yet unfair to the others that have called as he has new info but they also made illegal bets and didnt notice. because the small bling gets punished if you let the raise stand.