They

"Pants" is always plural, so you talk about them using "they" and "those".

a bit snug around the waistline

The word "snug" means "tight", but in a positive way:

Make sure that all the straps on your backpack are nice and snug. If they're too loose, everything will move around a lot more and you'll get tired out more quickly.

But in the example at top, the speaker uses "snug" to describe her friend's pants being too tight. In other words, she's saying that her friend is fat. This isn't very positive. But people also use "snug" to describe something that's tight in a bad way, if they're trying to sound polite:

Our hotel room was nice. The bed was a bit snug, but otherwise it was all great.

When people use "snug" in this way, they often say "a little snug" or "a bit snug".

The "waistline" is the area around your stomach where the top part of your pants are.

don't you think?

Use this question to ask for agreement from a listener. People use this expression when:

• they're making a suggestion:
  

  You should ask the professor for help, don't you think?

• they want to state their opinion, but they don't feel confident enough to just directly say it
• they want the listeners to feel included in the statement
  

  Wow. I love this place. It's great, don't you think?

• they want the listener to admit that something is true:
  

  You're too old for that, don't you think?