flimsy
adj.adj. describes something that is thin, weak, and breaks easily. You can also use it for an excuse or argument that is not very convincing.
adj. characterised by a lack of physical strength or structural integrity; easily damaged. When applied to abstract concepts like evidence or excuses, it indicates a lack of plausibility or persuasive force.
The flimsy table broke when I sat on it.
The suspect provided a flimsy alibi that the detectives easily disproved within an hour of the interview.
Constructed from flimsy materials that were never intended to withstand the coastal winds, the temporary pavilion collapsed during the first autumn storm.
The origin of the adjective is uncertain; it is possibly from flim(-flam) (“(noun) false information presented as true, misinformation, nonsense; poor attempt at deception, confidence trick, pretence; (adjective) frivolous, nonsensical; deceptive; fictitious”) or a metathesis of film (“thin layer of a substance; slender thread”) + -sy (suffix forming adjectives and nouns). The noun and verb are derived from the noun. Noun noun sense 4 (“metal container”) refers to the fact that the containers often split along their seams and leaked.
Often used both literally for physical objects and figuratively for arguments or excuses.