People who deliberately lose.

Yes, that would be sandbagging.

Dude I played my last game made a few ridiculous moves then quit, twice in a row. His best rating is 1700+ but he's worked his way down to sub 1400. He's 'lost' 25+ games in a row!

Sometimes people will have a rating that is too high, such as winning often against an opponent that has an inaccurate rating. Then there is no where to go but down.

Sometimes they might lose on purpose if they feel their rating is too high and it does not reflect their true ability and wish to play people that are easier to beat.

Sometimes they simply are having a bad stretch of games.

But no matter what deliberately losing is what resigning is. When someone resigns, they intentionally deliberately lose. Which is why some people never resign, they dont want to deliberately lose.

This dude was out and out losing on purpose. Now he's playing like a hero.

I see no point in sandbagging. If the purpose is to beat an easy player, u've just lost 30 games in the process. If ur goal is to get a high rating, u have to lose 400 points 1st.

And I'm not sure that I agree with you about people's rating not reflecting their true ability. Sure, you might get lucky in a few games, but surely the whole point of the rating system is that it reflects your ability level? How would it get to a certain level with having the ability to beat simarly rated people?

But winning 30 games will get u back up to normal rating anyway

It can happen by losing on time. I have had stretches of a dozen games that I would have won or drawn, but lost on time. So my rating went way down even though my ability did not. I don't play very many games here anymore but when I did, it was always 3 or 5 min games so I would lose on time a lot. Of course I could play longer games, if my schedule allowed, but my opponent would have more time also, which means the result might not have changed at all. With more time, and more complex positions at the end of the game, I could still easily lose on time.

 https://www.chess.com/forum/search?keyword=sandbagging

My blitz rating is almost 400 points higher than my bullet rating. U need at least 3 min to play a chess game

It is called sandbagging, but I dont know why that its bad at all, at least in online games and no tournaments it should be ok for 2 reasons:

1) He lose 30 games in a row to decreased his rating but he help 30 players to improve his rating and that is going to make them play against stronger people and improve

2) Once he have the low rating he play against lower opponents but that is good for them, playing against someone stronger is something really good for everyone, I love when I played a Titled player here that has over 2000+ 

This is only in online games that doesnt matter a lot, in real games and tournaments this is bad, because it cost money and the guy that cheat like this usually wins the prize and it isnt fair, there are some players that are like this and they lower the fide rating in order to play in a lower category than theirs, so if they are a 2000, the can play in a tournaments for -1800 and win most of the times

3 reasons I don't sandbag:

1. When I see a good move I can't resist it

2. I want my stats to be accurate

3. I want my rating to go up

No, but deliberately winning is a form a rating abuse.

Absolutely. I should have, and did, lose on time. Usually by just a few seconds. But with those dozen losses came a dozen wins for someone who could have just as easily lost or drawn all of those games. So now his rating is 100 or more points higher than his ability. So when he plays someone at his new rating, odds are his ability will not keep up. It's just an example of how someones rating may not reflect their ability. Over time and many games of course it mostly equals out. Thats why they have different ratings for different time controls. As Endgame said it takes at least 3 minutes to play a chess game. For me I was very often good at 3m15second games. That's not worth much in a 3 minute game.

What needs to be practiced to win easily won positions is simplification and quick decision making:

If u have 2 secs left with no increment, how do u pre-move fast enough to win. If the DTA is over 20, u have 0 chance of winning

 not sure if I happened to fall under 1.400 but I guess I did, it may happen I'm not sure how... when I recovered I made my record and I went all the way up to 1770 or so... 

It just happened to me again I',ve been quite inactive for a while and when I resumed to play I kept loosing points, this time I went under 1.500 but I lost some game on pourpose because someone got me nervous... still after that I struggled to come back to 1.500 and I got stucked there for a while, then again I really don't know how I gained around 150-200 hundreds points in a couple of days and I bounced back to 1.700.

so falling down in ratings may happen, 25 loss in a row looks suspicious though...

what's DTA?

Distance To Mate