You want something like a ... Creditcard or so?

if (% $+ $nick > = 100) {
.Describe $chan ~The bartender shakes his head and continues wiping down his glasses, \"Sorry there $nick you have racked up too high of a tab. I can\'t serve you anymore until you pay me.\"
}

Try the following

if (% [ $+ [ $nick ] ] > = 100) {
.Describe $chan ~The bartender shakes his head and continues wiping down his glasses, \"Sorry there $nick you have racked up too high of a tab. I can\'t serve you anymore until you pay me.\"
}