If you say that something is, for example, screamingly funny or screamingly boring, you mean that it is extremely funny or extremely boring.
[emphasis]
...a screamingly funny joke.
screamingly in British English
(ˈskriːmɪŋlɪ)
adverb
extremely
It's all so screamingly boring.
a screamingly funny story
I think the answer is screamingly obvious.
extremely in British English
(ɪkˈstriːmlɪ)
adverb
1.
to the extreme; exceedingly
2.
(intensifier)
I behaved extremely badly
▶ USAGE In strict usage adverbs of degree such as extremely, too, quite, really, and very are used only to qualify adjectives: he is very happy; she is extremely sad. By this rule, these words should not be used to qualify past participles that followthe verb to be, since they would then be technically qualifying verbs. With the exception of certainparticiples, such as tired or disappointed, that have come to be regarded as adjectives, all other past participles are qualifiedby adverbs such as much, greatly, seriously, or excessively: he has been much (not extremely) inconvenienced; she has been excessively (not too) criticized