#7 - Oct. 28, 2008, 5:32 p.m.
Yes you can delete them. While I do not recommend getting rid of the ones that are harder to pickup, you can even delete them before hitting the 25 tabard mark. I bought all of the easy to get tabards like Cenarion Expedition, Skyguard, Ogri'la, etc. and ended up at 24. So I sold these easy ones while I worked on the last one. Once I picked up the last one I got the achievement without re-purchasing the ones I sold.
Once again though, I recommend not getting rid of any of the difficult ones to get in case this doesn't work out as planned. But grats to all those who are real achievers!