Let's disregard for a second that there couldn't possibly have been any comments while this was happening, since no one can have known about the off-table bets. If you said something, what would you say?

"Stop betting so much, it's 1/2 and I don't feel like putting that much in the pot every hand without seeing the flop?"

"I don't like that you have an off-the-table agreement, so quit it or else"?

What would "or else" be in that case? What could you possibly do about it, instruct the floor to tell them to stop making it whatever amount they wanted in a No Limit game?

You mean if they had sat down and announced their "agreement"? I'm not clear on your scenario.

Well, as it actually happened, I'm trying to say it's impossible for anyone to have said anything to them since the off-the-table betting part of it was only revealed after they left. As it was occuring, all OP and anyone else thought were that there were two loose, wild players shoveling it in, which can be annoying to the recreational player but isn't illegal or unethical at all.

I guess you can take the scenario in which they announce at the start that they have a side prop bet. If this happened, yeah you could say something, although I don't know why anyone would, it's $40 in 1/2 going into the pot preflop with what are mostly terrible hands, this is a dream scenario for a good player.

I wouldn't say anything during their raise-fest.

Afterwards, once they admitted what they were doing, I would tell them they were jerks and next time they should just go the the restroom and share a stall.

Fair enough, would be justified, although their play in theory is still welcome because they're spewing

I know if this was happening at a table in my local casino, they would be a huge waiting list for the game. At the casino, I play at there is generally a bunch of 1/2 games and one "big" PLO game with a biggish list and often when the PLO guys play Holdem, they play abit like this.

I guess TECHNICALLY its against the rules of the game but I wouldnt really call it collusion b/c (IMO) its very -EV for them if the other players are moderatly competant and able to adapt.

OP, how many hands approx did this go on for?

you've gotta be pretty bad at poker if you're complaining about this going on at the table.

I'd be cool with it if they told the rest of the table that when one of them raises for less than 20, the other has to call with any hand. The two of them have that piece of information, the rest of the table does not. That makes it collusion even if they have no malicious intent.

All it does is hurt them though.

Maybe an 1 1/2 hours - so 50 or so hands

It was funny watching them - They wanted to buy in for more than the table maximum but the dealer wouldn't let them, so they bought a bunch of chips, put 300 on the table, put the rest on a drink table, and then keep topping off. They also had huge rolls of 100's that they pulled out to keep reloading.

They also didn't want to tip the dealer from their stacks. Instead they had separate stash of chips they kept in the drink holders to tip out of. As it turns out, the reason they didn't want to tip out of their stacks, is that it would effect their total win amounts regarding the prop bet. There must of have been a large amount of money on the prop bet for a dollar here or there to make that big of a difference.

I don't really see a problem with it, unless you could detect some sort of collusion designed to profit from the other players at the table for their mutual benefit. But from what you described they were
a) not colluding for their mutual profit
b) they were playing -EV poker

So I don't see any problem with it. I'd welcome it at my table.

What does that have to do with it? What if someone went to the table on a bet that he had to shove all in blind on every hand? What difference does it make if someone gets lucky or unlucky against that player?

Not sure I agree with that. This is wikipedia's explanation of collusion, which is not definitive as written, but note every example is something that gives the players in question +EV. In the OP's example, nothing like that happened.

"Collusion is two or more players acting with a secret, common strategy. Some common forms of collusion are: soft play, that is, failing to bet or raise in a situation that would normally merit it, to avoid costing one's partner or friend money; whipsawing, where partners raise and re-raise each other to trap players in between; dumping, where a cheater will deliberately lose to a partner; and signalling, or trading information between partners via signals of some sort, like arranging their chips in a certain manner."

That's because you seem to think "collusion" means "agreeing with another player to a certain style of play or strategy". Obviously some of us don't think that's a valid definition of collusion.

For example, let's say you and I sit down at a poker table and agree ahead of time that if the tightest player at the table shoves all in, we will both call him but only if our hands are hopelessly weak. Is this collusion?