1. Do you mind if I use the bathroom?

2. Would you mind if I use the bathroom?
3. Would you mind if I used the bathroom?
-----------------------------------
Which one is correct, #2 or #3? Use or used, should we use?

Well, probably #1 and #2 are best. Three is past tense, so it implies that the host might "mind" AFTER the bathroom was used. The question indirectly asks permission to use the bathroom in the present.