My son recently completed training for his third year of altar serving and brought home a notes sheet. It explicitly forbids servers from crossing their legs. I can understand a practical reason for this, given that altar servers wear a skirted garment, but it got me wondering. Am I showing disrespect to the Eucharist by crossing my legs when I am sitting during Mass?
No. Altar servers are up on the altar, in full view of the congregation, engaged in public ritual action. That is why their movements and postures are strictly prescribed and why certain informal postures are not appropriate for public ritual participation. None of this applies to laity in the pews. So long as you are not lounging in the pews, flopped back like you were at the beach, no one is going to care if you cross your legs.