Something that's fugacious lasts a very short time. You say you'll wear your trendy new jeans for years but the truth is, their style is so fugacious you'll feel silly in them long before they wear out.
When you describe something that passes quickly, or that's ephemeral and fleeting, you can use the adjective fugacious. When you live in Maine, the summer seems fugacious, and after looking forward all year to your senior prom, you'll find the night so fugacious that it seems to last only an hour. The origin can be traced back to the Latin word fugax, which means "apt to flee, or timid."