Shane and Ilya celebrate anniversaries with a frequency that baffles their friends. They just love having a reason to celebrate the fact that they made it through all the bullshit and now get to love each other openly.
Ilya maintains that the wedding with the Pike children is their wedding anniversary, while Shane insists that the day they got legally married is. Consequently, they each plan the celebrations on the day they feel counts (and it is a constant competition of trying to one-up what the other one planned).
Shane is also of the belief that their relationship anniversary is the day Ilya called himself Shane’s boyfriend for the first time but Ilya counts from their conversation in Tampa, which is when they became exclusive (regardless of the fact that this was not discussed between them). Again, they celebrate both days.
They both want to celebrate the first time they told each other they loved each other but Ilya insists that the time he said it in Russian over the phone counts, so two separate anniversaries it is.
Ilya insists on celebrating the first day Shane flirted with him and Shane agrees because the first day they met is a special occasion, although he still maintains he wasn’t flirting ("Shane, you shook my hand twice" "I am not having this argument again"). So they also mark their draft day, as the first day Shane picked up on the fact that Ilya was flirting.
Of course they celebrate the CCM shoot day, it was their first kiss, their first sexual experience together, the day everything changed, but they also celebrate their anal-versery and the first time they fucked without condoms.
Ilya insists on marking the day they met on the ice for the first time as the first time he beat Shane, so Shane decides the day he won Rookie of the Year (the only award either of them has that the other has no chance of ever winning) deserves to be celebrated.
One time they said they couldn’t make it to post-game drinks because it was their anniversary and Troy asked, “oh, which one is it this time?” only to find out they were celebrating the first time they had phone sex. After that the Cens learned not to ask questions.