Yes, you can drink coffee before your tattoo appointment, but I wouldn’t recommend having much more caffeine than you normally do. If you already drink coffee every day, your usual amount is generally fine.

The bigger problem is arriving on an empty stomach with only coffee. For a long session, eat a proper meal and drink water as well. Too much caffeine can also make you feel more restless during a session, which is the opposite of what you want when you may need to stay still for several hours.