Echoing falsifiedhypothesi, when your on benzos your uninhibited and often have bad judgement. Adding a stimulant can lead people to attempt things they really shouldn't on benzos, like driving, calling your ex, telling your boss what you really think of him, etc.
If you aren't experienced with benzos just chill and don't try to engage the world to much. Stimulants, even lots stronger stuff than coffee, don't render you unaffected by benzos.