For the sentence, 你别乱闹. I think it means "do not randomly complain," but that doesn't sound right. I can't pinpoint what 乱 means.
2 Answers
乱 (adv): arbitrarily
on the basis of random choice or personal whim, rather than any reason or system.
without restraint in the use of authority; autocratically.
Example:
乱花錢 = spend money arbitrarily (randomly, without restraint)
乱闹 = arbitrarily (without reason, without restraint) making trouble
乱猜 = arbitrarily (randomly) guess
乱説 = arbitrarily (without reason, without restraint) say
乱 (adv) = 随意地/ 随便地(randomly); 武断地 (arbitrarily); 胡乱地 (indiscriminadamentely)
In 《现代汉语词典（第七版）》, one of the senses provided of 亂/乱 is
... 5. <副> 任意，随便 | at random, haphazardly
And in Wiktionary, we have this:
... 8. wildly; in an uncontrolled way; without order or reason; at random; haphazardly; having no direction or coherence; recklessly
亂說 / 乱说 ― luànshuō ― to say whatever is on one's mind
亂舞 / 乱舞 ― luànwǔ ― to dance in an unorganized, uncoordinated way
another way to say 乱闹 will be 胡鬧/胡闹 (Click to see the Wiktionary page).
More examples:
你别乱来 (or 胡来)。 Don't mess around.
你别乱说 (乱讲, or 胡说)。 Don't talk nonsense.
这个词可不能乱用。 This word must be used in the proper way.
那个人在到处乱跑。 That person is running all over the place.
