I've made some really crappy tabs back when I was a total guitar noob, so I really want to delete them. NOW.
As far as I know, the only thing you can do with existing tabs is updating them. I haven't seen any option to delete existing tabs.
Mate, I know exactly how you feel. The thing is the other tabs sites leech from UG so even if you delete it from UG, they'll still be everywhere on the Internet. So just consider it lesson a learnt.
Nope...can't delete them... I am the same as you as far as posting bad tabs way back when...but it is what it is... No big deal... The only thing you can do is update the tab if it is on UG or redo it and resubmit it.... Then possibly go back to the old one and remove all the tab and leave a statement saying that your removed it but have put a better updated version of it...
Best thing to do is just not worry about it and like I said either update it or make a complete new one and resubmit it...

Truthfully, any tab out there whether it is good or bad helps out some..especially if there is no other version of it...