Why do women always want to go to the bathroom together? Totally incomprehensible.
Literal
Women [casual topic-って] why group-bathroom want-to-do [question-の]? Incredibly incomprehensible.
連れション (going to the bathroom together) is vulgar slang — ション abbreviates 小便. ~たがる describes a third person's desires, since ~たい alone can only express the speaker's own wants. って marks the casual topic. 物凄く (incredibly) intensifies the blunt 理解不能 (incomprehensible). A rawly casual, gender-commentary sentence.