I really enjoy the service in Colombia for the most part, I've never really been bothered by this as it's usually a small amount anyway. If the service is really good I'll just round the bill up. Personally the propina to me added to the bill seems more like a tax so I kinda just know if my bill is 23,500 it's gonna go up but it'll be under 30,000. If you really object to this, try to refuse it, otherwise just don't tip over top of it. I can tell you they don't expect it, though they might expect it more at an american brand place ie: Hooters in MDE, I feel like there's probably alot of gringos going through there and tipping.