From 绷不住了, bēng bù zhùle, literally "unable to stretch anymore". Means to be pent up and unable to hold back (such as in sexual urges, laughter, or anger). Basically means, "I can't help it".
When you try to tag someone on Facebook but their name does not appear in the tagged photo and/or status post. This person may have opted out of being tagged in anything due to the increasing fear that unwanted friends, enemies, insurance agents and employers or prospective employers might see something they wish to keep private.
I tried to tag Sam and the two sisters but Facebook wouldn't let me. I guess they're untaggable.