one answer is at least kind of straightforward:
🀅 🀫🀀🀀🀫🀫🀁🀁🀫🀫🀂🀂🀫🀫🀃🀃🀫 tsumo/ron: 🀅
four closed kans of each of the winds plus any dragon pair wait yields a sextuple yakuman, the maximum possible under the standard scoring rules. specifically...
this comes out to 192,000 points, or 288,000 if you're the dealer. this is more than enough yakuman to guarantee someone busts out, no matter how perversely balanced the players' scores are. amazingly, this hand has been achieved before!
if upgrading all four of your wind triplets to closed quads sounds a little impossible to you (it does make the already extraordinarily unlikely hand about 2,000 times less likely), you can settle for a quintuple yakuman without the quads. or just draw your wind triplets and dragon pair at the start of the game and get blessing of heaven/earth (tenhou/chiihou) to bump it back up to sextuple! no skill required.
so, okay, that's fun and all. but let's say you're not looking to win big - rather, you just don't want to have to pay for any big wins from your opponents. that's what the rest of this post is about: what's the most you could have to pay in a round of riichi mahjong?
first, you should know that you can be ron'd by multiple players, if your discard completes all of their hands. in 4-player, it's possible to get ron'd by all three of your opponents! so, let's start by assuming the opponent to your left is the dealer, and they complete their sextuple yakuman hand shown above using your ill-advised green dragon discard. how about the other two players?
the most obvious way for them to rack up points is four concealed triplets with pair wait (suuankou tanki), which can use triplets of any four arbitrary tiles, as long as they're waiting to complete a green dragon pair . this would give both of your non-dealer opponents a double yakuman, costing you 64,000 points each. can we do better?
all terminals (chinroutou) and nine gates (chuuren poutou) won't work here because they exclude honor tiles, and changing the dealer's honor tile pair wait to a number wait would subtract their more-expensive all honors yakuman for the sake of adding a less-expensive non-dealer yakuman. we also can't give more players four kans, because any further kans would end the game in a draw. we also don't have enough honor tiles left to form a second all honors hand.
we can't even use the remaining white & red dragons to give someone big three dragons (daisangen), because that player would have to be holding two green dragons in order to complete the triple with your discard. there are only four of each tile, so we've exhausted our green dragons before we've gotten to the last opponent. the only way for someone to ron you for an honor tile that's not in their own hand is with thirteen orphans (kokushi musou), which would have to replace four concealed triplets, decreasing the value by one yakuman since it couldn't be 13-wait. thirteen orphans is presently impossible anyway since all the wind tiles are accounted for, so both it and big three dragons are definitely out.
there is one other yakuman that can stack with four concealed triplets, though: all green (ryuuiisou). so, let's take one of the non-dealer opponent's hands to be as follows:
🀑🀑🀑🀒🀒🀒🀓🀓🀓🀕🀕🀕🀅 ron: 🀅
the final opponent's hand doesn't have any other yakuman to stack with, sadly, so it's just four arbitrary triples and a green dragon pair wait. let's go with this for completeness:
🀊🀊🀊🀞🀞🀞🀠🀠🀠🀆🀆🀆🀅 ron: 🀅
the addition of all green bumps that opponent's hand to a triple yakuman, costing you 96,000 points. combined with the 288,000 point dealer hand and the remaining player's 64,000 point hand, you're paying a grand total of 448,000 points for that single discard, nearly 18 times your starting points. this obviously unconditionally busts you out, and probably also totals your ego.