It's ketchup and mayonnaise mixed together, so...
5 seconds sound clip from the Step Brothers (2008) movie soundboard.
You can hear this line at 00:08:40 in the Blu-ray version of the movie.
Quote context
[...]
- You might wanna try this. I make a sauce, we call it fancy sauce...
- For me.
- Brennan really likes with his chicken nuggets.
- Well, when Brennan finishes, I'll give you some of this...
- It's ketchup and mayonnaise mixed together, so...
- Yeah.
[...]