Best Episodes to Show a Newbie?

Sorry if this is the wrong place to ask, but I had a question about this show. For Christmas my brother asked me to write a fanfiction about two of the show's characters since he likes my writing and he's been binging the series with his girlfriend. I know next to nothing about the show, and I was hoping someone could direct me to the best episodes to watch to get a feel for it.

If it helps, his two favorite characters are Mac and Dennis. Any recommendations for the best episodes to watch to get a feel for the group's personalities or the sense of humor would be greatly appreciated. I thought of googling just the "best" episodes in general but I didn't feel like that would be subjective enough. I also didn't ask my brother because I want to keep from possibly spoiling whatever I decide to write.

To summarize, I'd like it if someone could tell me what episodes they'd recommend to someone starting the series blind that doesn't include the first episode. I just feel like pilots don't accurately convey the vibe of a TV show, especially a long running one like IASIP. Thanks in advance!