I believe that the correct sentence is: "My last birthday was the worst day that I HAVE ever had (so far in my life)." Since you are still living, it is possible that in the future you may have a day that turns out to be even worse than your last birthday. So we should use the present perfect. Compare: That movie I saw yesterday was the best movie that I HAVE ever seen (so far in my life).

hello) to tell the truth i never used Simple Past+Present Perfect ! In the University we were taught that we should use present tenses with present tenses and past tenses with past tenses(The Sequence of Tenses rule)

1st sentence - use it is you are comparing the past to your ongoing life. "That was the worst day I have ever had." (There has never been a worse day before or since then.) 2nd sentence - use it is you are comparing the past to your life in the past. "That was the worst day I had ever had." (When it happened, it was the worst day of my life, but I've since had worse days).