I think it's pretty safe to buy an onahole.
I'd like to ask again AkaiHebi if he is sure about to having to open it in front of the postman in Germany, like, you have to go to your post office, open it there and then take it? It does not make much sense to me, I think they will just open it un customs, close it, and ship it to your house as a normal legal packet.
You are safe to buy small onaholes, try not to surpass 60€, or you might be risking taxes, I say 60€ because I never surpassed ~65€ or so and did not get a tax. Smaller orders rarely get in customs, and even if they did, I doubt they'll give you a phone call, if it's legal, there should not be a problem. Either way only give YOUR phone number to the shipping company so customs call you instead of you parents, but I doubt they will call you. Maybe they will send you a letter, in case something goes wrong. If you want big onaholes like this one, maybe it would be safer to ask them to remove the package as how AkaiHebi did.
Look around the /b/ board and see people showing pictures of their orders, I've made +10 orders so far to Spain and 0 problems, once I ordered for 115€ and had to pay 35€ taxes to the postman. Everything it's completely safe, no one will know what's inside except customs maybe, so go ahead, I think everything will be ok :)