Or maybe if they went to the past wearing Levis... but that'd be crazy.
Actually I like that idea. Levi's were invented in 1853
and there is no reason not to believe that 150 years from now that people may also be wearing them.
Some people IIRC in this thread have criticized the bar scene from Trek X as to 21st century and not a place where people in Star fleet may hang out.
Whomever said that has never lived near a Naval base because if they had and went to a local bar - a scene not to dissimilar would occur today, 50 years ago or even 100 years ago. So it's likely that a bunch of young SF recruits would be hanging out at a seedy bar.