Hail to the Chimp

A quick way to get this and Also-Ran using 4 controllers:

Select a 4-player game. With your GamerTag-associated controller, choose Floyd. With controller 2, select Crackers. With the other two controllers, select any other characters.

Choose an easy board (I suggest the waterfall board) and a gametype that is not skill-based or danger-based. (I recommend the one where you collect sets of clams.)

Use your first 3 controllers to collect a few sets of clams.

Team up with Crackers, and once the team-up expires, kill him.

Team up with controller 4, and just let the team-up expire.

Repeat, alternating between Crackers and controller 4. (You cannot team up with the same player back-to-back.)

Once you have done this 25 times, finish the game, and the achievements will pop in the post-game analysis.

the best way to do this is make sure you have 4 players and make sure you use any of the combos of rivals for when you play. then team up wiht your rival and imediatly after the team up kill them. in some cases it may take a few hits to kill them so what you want to do before you team up with your rival is hit them until there star beneath there feet is flashing red then team up and in one hit you will kill them. do this 25 times and thats it!

Some Friend - Betray 25 Team-ups.

Even though the description says to simply betray 25 team ups it is more complicated than that. What you have to do is actually betray 25 team-ups with your characters RIVAL. When the achievement pops the description actually says rival. So what you do is team-up with your rival and attack them immediately after the team up ends. This can be done with multiple remotes in vs mode to make it easier.

As a side note, this achievement will not pop during the primary it will pop at the end. The rivalries I am aware of are:

Floyd - Crackers
Murgatroyd - Toshiro
Daisy - Santo