What you need depends on what you want to do.
Using the || will match in all cases apart from when the nick contains both those "words"
From the command line you can test out the logic.
//var %nick = myfriendfishbot | if (myfriend !isin %nick) || (fishbot !isin %nick) { echo -a true }
//var %nick = myfriend | if (myfriend !isin %nick) || (fishbot !isin %nick) { echo -a true }
etc.
Change the %nick variable's value to what ever, it will echo true when its true, else it will do nothing.
Failing that, google for truth tables. I'm sure there is something there that will show you how to draw one up.
They really help to gain understanding and find better equavilant if tests that might be more efficient in many situations.
If its the && thing you want, using the previous else if you have, you can just use "else"
