I Secretly Refill My Own Drink

So, here's something I feel really awkward about admitting. When it's slow at work and there are drinks sitting around waiting to be picked up by customers, sometimes I sneak a sip or two of them myself. It started as just tasting different flavors for fun but has turned into me needing an energy boost mid-shift. And yes, once or twice, I've even taken the last bit of someone's drink that they forgot to take before leaving. This probably makes me seem like the worst barista ever, and every time I think about how dishonest this is, it gives me such a bad feeling in my stomach. But the irony is, when customers complain about something tasting weird or being short on ingredients, I know exactly what's up but can't tell them the truth without getting fired. This little habit of mine feels like a constant nagging guilt weighing me down.