ARE STRAIGHT MEN ALLOWED TO BUY B-DAY CARDS FOR CO-WORKERS?

Okay -

In EVERY SINGLE OFFICE I'VE WORKED IN, the cake, birthday card, etc is ALWAYS purchased by a woman or the gay guy there. Are straight men fundamentally not allowed to do these things for their co-workers? Is it an unspoken rule? Will you be forevermore labeled as "sissy boy" if you walk into the workplace with a bundle of balloons and an ice cream cake from Baskin Robbins?

Come on men - speak up!