Revealing mistake: When the first sumo takes off his "diaper" and throws it in the basket, you can see he is still wearing something.
Plot hole: How can Austin's Father be so young? Don't forget that Austin was frozen for 30 years, so their age gap should be 30 more than normal; but despite that the age gap between them seems about normal for a father and son.
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Suggested correction: This used to drive me nuts as well, until my latest viewing when I realised Goldmember first kidnaps him in 1975, and brings him to the future. As for Nigel missing Austin's award, maybe in the first timeline Nigel lives to be 95 ish.
Suggested correction: Nothing indicates in the film that sumos are necessarily naked under their layer.