How I Met Your Mother: 10 Worst Things Robin Ever Did
9. Halloween Behaviour
Although it may seem oddly specific, there are a couple of things regarding Halloween celebrations where Robin shows herself up.
Early on, she point-blank refuses to dress up in a costume for the celebrations. Not a huge issue in and of itself, but she goes on about it a little too much and insults everyone else for being into it. It's especially harsh on people like Lily and Marshall, who love the holiday, but Robin is so insistent on telling everyone why she doesn't want to dress up that she'll happily stomp all over the feelings of people who are allegedly her friends.
In addition, the first Halloween party that we see her at is also the genesis of another character flaw - the way she treats her partners. At this first Halloween party, she is extremely unkind to the man that she's brought there as her date. Every single time he refers to them as "we", she objects and cuts him off.
Again, not an issue if it isn't working out with a date - but why take him along and cut him down in front of all her friends? Because she's Robin. That's why.