茹蛸	4280	34.5%
茹でタコ	2864	23.1%
茹でダコ	2788	22.5%
茹で蛸	2076	16.7% <- most references
茹だこ	42	0.3%
茹ダコ	365	2.9%
GG5: a man as red as a lobster.
中辞典: グラス 1 杯のビールでゆでだこのように赤くなる go as red as a boiled lobster after a single glass of beer.

The JEs all like the lobster version.
I'm demoting the 茹蛸. While it's the most common single term, the term is most commonly 茹で[蛸,ダコ,タコ].

@@ -4,3 +3,0 @@
-<k_ele>
-<keb>茹蛸</keb>
-</k_ele>
@@ -16,0 +14,3 @@
+<keb>茹蛸</keb>
+</k_ele>
+<k_ele>
@@ -17,0 +18 @@
+<ke_inf>&sK;</ke_inf>
@@ -20,0 +22 @@
+<ke_inf>&sK;</ke_inf>
@@ -23,0 +26 @@
+<re_restr>茹で蛸</re_restr>
@@ -25,2 +27,0 @@
-<re_restr>茹で蛸</re_restr>
-<re_restr>茹だこ</re_restr>
@@ -36 +36,0 @@
-<re_restr>茹ダコ</re_restr>
@@ -39,0 +40 @@
+<re_restr>茹で蛸</re_restr>
@@ -41 +41,0 @@
-<re_restr>茹で蛸</re_restr>
@@ -52 +52 @@
-<gloss g_type="expl">person with red flushed skin (esp. due to a hot bath or alcohol consumption)</gloss>
+<gloss>person with red flushed skin</gloss>

daijs:  風呂に入ったり、酒に酔ったりして赤くなったさまのたとえ。 「怒って茹で蛸になる」
sanokoku:入浴や飲酒などで赤くなった人 

https://en.wiktionary.org/wiki/red_as_a_lobster#:~:text=Adjective,synonym ▲ Synonym: lobster
Bright red in color, especially from a bad sunburn

https://forum.wordreference.com/threads/as-red-as-a-lobster.3243268/
As lobsters (at least boiled ones) are red all over their body, "red as a lobster" is usually used when someone has been sunburned particularly all over their body

https://forum.wordreference.com/threads/as-red-as-a-lobster.2979095/
I hear it mostly when people talk about sunburn.
Also, if you want to say that someone turned red from embarrassment, you can say that they turned "beet red." (My mom uses this one all the time.)

https://www.cntraveler.com/stories/2007-05-02/onsen-zen
. The Japanese consider that bathing nirvana is achieved at the yudedako, or "boiled octopus," stage. Place a folded washcloth on your forehead to keep cool.

https://www.japantimes.co.jp/life/2003/04/20/travel/seeking-tranquillity-in-tohoku/
 The region used to be known as Michinoku, meaning, ... onsen bath in Japan to complete that essential yude-dako (boiled octopus) look.


https://detail.chiebukuro.yahoo.co.jp/qa/question_detail/q138593103
お風呂に入っていると、ゆでだこにならないように言われます
なんで茹でタコと言うのですか

タコはゆでると真っ赤になるので人も長湯でゆでだこみたいに
なるよ！というのです。

I am not the only one who thinks "red as a lobster", if anything, means "sunburned all over ones body".  I don't think these idioms match, which makes this a misleading gloss.

I'm not sure we have a useful idiomatic substitute. The explanation for the idiom is apparently (see last ref) that octopuses turn bright red when boiled. So the connection to hot baths is not arbitrary. Both dictionaries call out baths and alcohol specifically.　Can also refer to alcohol-induced flushing, and anger, etc.  No apparent connection to sunburns.

I imagine "alcohol" applies due to the Japanese genetic disposition toward alcohol intolerance(cheeks may flush red).  Westerners don't turn red from drinking (generally). 

We also don't have a hot-bath culture, so we seem to be lacking for a truly equivalent idiom.

Here's an illustrated octopus with a towel on its head in a bath:
お湯に浸かって茹蛸になるタコ
https://www.ac-illust.com/main/detail.php?id=1069549&word=お湯に浸かって茹蛸になるタコ&searchId=

Here's an angry octopus: 怒るタコ / ゆでだこ
https://japaclip.com/angry-octopus/

@@ -52 +52 @@
-<gloss>person as red as a lobster</gloss>
+<gloss g_type="expl">person with red flushed skin (esp. due to a hot bath or alcohol consumption)</gloss>

@@ -50,0 +51 @@
+<misc>&id;</misc>

茹でタコ	2864
茹でダコ	2788
茹蛸	4280
茹で蛸	2076
茹だこ	42
茹ダコ	365
茹たこ	41

@@ -3,0 +4,3 @@
+<k_ele>
+<keb>茹蛸</keb>
+</k_ele>
@@ -9,3 +11,0 @@
-</k_ele>
-<k_ele>
-<keb>茹蛸</keb>
@@ -22,0 +23,6 @@
+<reb>ゆでだこ</reb>
+<re_restr>茹蛸</re_restr>
+<re_restr>茹で蛸</re_restr>
+<re_restr>茹だこ</re_restr>
+</r_ele>
+<r_ele>
@@ -31,6 +36,0 @@
-</r_ele>
-<r_ele>
-<reb>ゆでだこ</reb>
-<re_restr>茹蛸</re_restr>
-<re_restr>茹で蛸</re_restr>
-<re_restr>茹だこ</re_restr>

https://www.japanesepod101.com/japanese-phrases/09232019?meaning

@@ -15,0 +16,6 @@
+<k_ele>
+<keb>茹だこ</keb>
+</k_ele>
+<k_ele>
+<keb>茹ダコ</keb>
+</k_ele>
@@ -23,0 +30 @@
+<re_restr>茹ダコ</re_restr>
@@ -28,0 +36 @@
+<re_restr>茹だこ</re_restr>