Definition:
Bummer is a slang term used to express disappointment, frustration, or sadness about a situation or event.
Use case:
You can use the word bummer when something negative happens or when someone shares bad news. For example, if your friend cancels plans at the last minute, you can say "Oh, bummer, I was really looking forward to it." Or if someone tells you that they failed an exam, you can say "That's a bummer, I'm sorry to hear that."
• I forgot my phone charger at home, what a bummer.
• It's a real bummer that I have a cold on my vacation.
• The news about the company's bankruptcy was a real bummer for everyone who worked there.
• It's a bummer that the concert got cancelled due to bad weather.
• Oh bummer, I spilled coffee on my shirt.
• It's such a bummer that I have to cancel our plans tonight because of work commitments.