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Kylie Jenner's video from Dream's second birthday party proves Auntie Kylie is the hostess with the mostest ... the mostest cockroaches.

Jenner hosted her niece's 2nd birthday party Wednesday at her Hidden Hills home ... and there was at least one uninvited guest patrolling the sweets table. The 6-legged party guest can be seen scurrying for cover underneath Dream's decked out bday cake.

As for how the critter may have entered the bash -- there are a ton of plants and foliage intertwined with the dessert spread -- so you gotta imagine he hitched a ride inside.