Are all tongue rings straight

No, they have to go in at an angle otherwise they could hit a major vein and you could loose all feeling and taste in your tongue.

The above information is incorrect.

Yes all tongue barbells are straight there is no need for a curved or bent barbell in a tongue piercing.

1. Tongue piercings done by a seasoned professional body piercer are done straight.
2. The tongue is two muscle complexes joined by connective tissue that runs down the "frenial line" or center line of the tongue.
3. The tongue has over 10,000 taste buds and the chances of losing the sense of taste is non existent due to a piercing.
4. The two muscle complexes that form the tongue each have there own major arteries and return veins seen on the under side of the tongue, as well as there own nerve bundles feeding the right and left side of the tongue.
5. Be sure to see a professional body piercer for all your piercing needs, the internet is full of misinformation so surf with care.

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I believe the question was referring to the jewelry itself, not the actual piercing process. Even if that's not so, some piercings are sometimes done at an angle to avoid the veins or at the piercee's request. The angle isn't usually an obvious one, unless you want a special piercing. Some people get venoms (also called viper bites, vipers, snake bites-depending on your region) and some get horizontal piercings instead of vertical ones.