When can I use "must have been?" Is it different from "should have been?"

What does the "podcast" mean?

A "podcast" is a series of audio episodes or files. They're usually put on a podcast or audio platform where people can access and listen to them. They vary in subject, form, and length. Ex: There's a new episode out from my favorite podcast today. Ex: I like to listen to podcasts while I work.

Can I say "attack" instead of "strike"? Or do they have different connotations?

They do have slightly different connotations! "Strike" is a single action or hit, whereas an "attack" could be more than one hit, and it could last longer. One can "strike" someone while "attacking" them. However, in this context, it would be fine to use "attack" instead of "strike", as they both indicate the beginning of a fight or attack. Ex: Are you ready? Attack! Ex: Just one more strike, and he'd be unconscious. Ex: Did you see the news? Someone was attacked last night. They had to go to the hospital. Ex: I was struck on the arm during a fight. Ex: Those bugs could attack at any moment. = Those bugs could strike at any moment.

Is the joke of toilet in this sentence often used?

No, not really. This is just an expression. She said "I'm going to just flush myself down the toilet" because she is extremely embarrassed that she thought Chandler was gay. "I could just die" is a more common expression for being embarrassed. English speakers may also use "I made a fool of myself" or some may even use "that will be egg on my face." These both refer to being embarrassed about something, but there are many kinds of expressions that are used.

What's the main difference between "disposable" and "expendable?"

If something is "disposable," it means that it can only be used once and then thrown away, or that you throw it away when it can no longer be used. But if something is "expendable," it means it is of little value or worth compared to a bigger purpose, so one doesn't necessarily need it. Ex: The flowers for the reception party are expendable compared to having live music during the event. Let's book the band first before getting flowers. Ex: We need some disposable cups and plates for the party, then we don't have to clean as much afterwards.

What does "Come up with" mean?

"Come up with" means to produce something, especially when under pressure. Ex: She came up with a great idea for her science project. Ex: I need to come up with a new plan. Ex: We should come up with ideas for her birthday party.