Why doesn't Denmark retaliate against the USA and attempt to purchase Hawaii?

Denmark is too poor to buy Hawaii. The offer to buy Greenland was not an attack on Denmark, so no need for a retaliation.

It's been 28 C in the shade here in Denmark today.

Anyway, attempting to purchase Hawaii would be futile, morally wrong, and way out of the Danish budget. Oh wait... I guess a bit like the USA purchasing Greenland. Besides, there's no need for retaliation. If all your friends jump off a cliff...

Big difference between attempting and asking or in this case, possible implying.

The US didn't attempt to purchase Hawaii. It never did, not from anybody. The US took Hawaii by force. The US had previously had a friendly relationship with Hawaii, fending of European powers from Hawaii, powers, like Britain and France, who had forced Hawaii into unfavorable trade agreements, but the friendly relationship between the Hawaii and the US, its protector, fizzled when Queen Liliuokalani took over and later started to become quite dictatorial, so the US, specifically President Benjamin Harrison, chose to have her deposed, dispatching sailors from the USS Boston and surrounding the palace. About five years later, in 1898, after several attempts to set up an independent government for Hawaii failed, the US annexed Hawaii. It became a state 50 some years later.